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Declining testicular function with age
Declining Testicular Function with Age Hormonal and Clinical Correlates
E. L. STEARNS,
M.Sc.
J. A. MacDONNELL,
M.D.
B. J. KAUFMAN, M.D. R. PADUA, M.D. T. S. LUCMAN, M.D. J. S. D. WINTER, M.D.’ C. FAIMAN,
M.D.’
Winnipeg, Manitoba, Canada
From the Departments of Physiology, Medicine (Geriatric Teaching Unit) and Paediatrics, University of Manitoba and the Endocrine-Metabolic Laboratory, Health Sciences Centre, Winnipeg, Manitoba, Canada. This study was supported by Research Grant 22-27-72 Deer Lodge Hospital, Department of Veterans Affairs, and M.R.C. Canada Grant MA-2997. It was presented in part at the Fifty-Fifth Meeting of the Endocrine Society, Chicago, Illinois, June 20, 1973; Gerontological Society Meeting, Houston, Texas, October 27, 1971; and the British Geriatric Society, Aberdeen, Scotland, April 12, 1973. Requests for reprints should be addressed to Dr. E. L. Stearns, G449, Health Sciences Centre, 700 William Avenue, Winnipeg, Manitoba, Canada R3E uZ3. Manuscript accepted February 15. 1974. * Queen Elizabeth II Scientist. 1 M.R.C. Canada Scholar.
Testicular endocrine function and androgen-dependent secondary Sexual characteristics were assessed in 283 men 16 to 96 years Of age. Mean serum total testosterone levels remained unchanged up to age 70 and declined thereafter. In 29 per cent of the men over 70 years of age total testosterone levels were below the lower limit of normal for young adults. In contrast, mean free or unbound testosterone levels declined after age 50 and were below the lower limit of normal for young adults in 40 per cent of the men over 70 years of age. Serum-luteinizing hormone and follicle-stimulating hormone levels showed a slight but steady rise after age 40 which became more abrupt after age 70. Serum gonadotropin levels were elevated in approximately 60 per cent of the men over 70 years of age. Mean testis length and volume were decreased in 76 per cent and 37 per cent, respectively, of the men over 60 years of age. Facial, pubic and axillary hair were also reduced in amount whereas the prostate was enlarged in 73 per cent of the elderly men. There appeared to be an inverse relationship in older men between testicular size and gonadotropin levels, and a direct relationship between testicular and prostatic sizes. It would appear that some degree of Leydig cell hypofunction commonly begins at around 45 to 50 years of age, becoming more pronounced after age 70. The concomitant elevation in serum gonadotropin levels at this time indicates that this is due to a primary decline in testicular function and is not secondary to pituitary hypofunction. The possibility of declining testicular topic for surmise and anecdote for systematic studies of this question vestigators have been unable to ences in mean serum testosterone whereas others and old men [l-3],
function with age has been a centuries, but surprisingly few have been reported. Some indemonstrate significant differconcentrations between young have reported a decline in ei-
ther serum total testosterone concentration [4,5], the free* or unbound testosterone fraction [4], or urinary excretion of testosterone glucuronide [7,8] with age. However, the observation that both serum and urinary gonadotropin levels are increased in at least some elderly men [S-10] may be evidence that declining testicular function with age is not uncommon. The clinical correlates of androgen production have been even less thoroughly studied in elderly men. Although prostatic size and
Unconjugated testosterone circulates in the blood either bound to serum proteins or in the unbound or free state. Evidence is accumulating which suggests that free testosterone is the biologically active fraction [6]. l
November 1974
The American Journal of Medicine
Volume 57
761
TESTICULAR FUNCTION AND AGING-STEARNS
ET AL.
the amount of facial and body hair are sensitive markers of the presence of androgens at puberty [ 11,12], the relationship between secondary sex characteristics and androgen concentrations in senescence are as yet undefined. Although there is his-
tologic evidence of degenerative changes in the aging testis [8], it appears that testicular weight and length do not change with age [ 13,141. The aims of our study were threefold: (1) to assess the relationship between androgenic function and aging by comparing total and free circulating testosterone levels in representative populations of old and young men; (2) to determine serum gonadotropin levels in these men in order to assess whether the suspected decline in testicular function is primarily testicular in origin or secondary to hypothalamo-pituitary hypofunction; and (3) to provide clinical data on testicular size and androgen-dependent sexual characteristics, correlating any changes in these features with hormonal alterations. MATERIALS
AND METHODS
Subjects. Two hundred eighty-three men aged 18 to 96 were studied. Of these, 142 were over the age of 60 and were drawn from the Geriatric Teaching Unit at Deer Lodge (Veterans) Hospital; the remaining 14 1 were healthy hospital personnel and Red Cross blood donors. For inclusion in the study each of the subjects over 60 years of age had no history of alcoholism, a physical examination within normal limits for his age, a normal urinalysis, a blood urea nitrogen level below 40 mg/lOO ml and a hemoglobin level above 11 g/100 ml. Forty of these men were taking occasional sedatives, 14 were taking digitalis, and 19 were taking both sedatives and digitalis. The men under 60 years of age were in good health and were not taking any medication at the time of study; they were not given a physical examination. Testicular Size and Secondary Sexual Characteristics. All measurements were obtained by at least two observers. When observations differed and the subject could not be reexamined, the disputed data were not used. In addition, some subjects refused either the clinical or the endocrine assessment. Testicular size was determined in 116 men both by measuring testicular length (mean of longest diameter of both sides in centimeters) with a rule and by estimating the mean testicular volume using the Prader orchidometer [ 151. Facial, axillary and pubic hair in 140 men was either normal or decreased in amount. Prostate size in 138 men was recorded as either normal or enlarged. Blood Samples. Twenty milliliter samples of blood were taken by venipuncture between 0800 and 1100 hours, allowed to clot and the serums frozen at -2O’C. All assays were carried out in duplicate. Gonadotropins. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were measured by radioimmunoassay [ 16,171. Levels are expressed in terms of the pituitary standard LER-907. Total Testosterone. Serum testosterone levels were
INovember 1974
The American Journal of Medicine
Volume 57
TESTICULAR
measured by radioimmunoassay [ 181 without column or thin layer chromatography, steps which were found not to be necessary for nonpregnant serum estimations. Per Cent Free Testosterone. The per cent free testosterone was measured by a modification of the method of Rosenfield [ 191; 1 ml 0.1 per cent charcoal 0.01 per cent dextran-80 (Pharmacia) suspension was used to separate bound from free testosterone. The intra-assay coefficient of variance between duplicates was f2.5 per cent, and the interassay coefficient of variance was f3 per cent. Correction for interassay variation was found to be unnecessary. Free Testosterone-Index. The free testosterone-index was calculated by multiplying the per cent free testosterone by the total testosterone concentration for each subject. Although determined under in vitro conditions, the index provides an estimate of the unbound testosterone concentration in vivo. Estradiol. Serum estradiol levels 1201 were measured by radioimmunoassay in 93 subjects over 60 years of age. Linear and log-linear correlations Statistical Analysis. [21,22] were determined among the variables of age, FSH, LH, total testosterone, per cent free testosterone, free testosterone-index, estradiol and testicular size. Each of these variables was also compared with the clinical variables in the subjects over age 60 years. The hormone levels of each of the clinical groups (those with normal or increased prostate size; those with normal or decreased sexual hair) were compared by an unpaired t test [ 2 l] Relationships among the clinical variables were assessed by Chi-square analysis [ 2 l] RESULTS In order to rule Effects of Digitalis and Sedatives. out a possible effect of digitalis, which may have estrogenic properties [23], or of sedatives on the variables studied, subjects taking one or both types of drugs were compared with their untreated peers. There were no significant differences among the
FUNCTION AND AGING-STEARNS
ET AL.
AGE (YEARS)
Figure 1. Serum total testosterone levels in men 18 to 97 years of age. The doffed line indicates the lower limit of normal for men less than 45 years of age.
age 50 (as opposed to age 70 for total testosterone) as a consequence of the decline in per cent free testosterone (Table I); and (2) 40 per cent ‘of the men over 70 years of age had free testosterone-index levels below 100, the lower limit of normal for young men. Gonadotropins. Mean serum LH and FSH levels (Figures 3 and 4, respectively and Table I) remained constant until age 40 at which time they began to rise. The rise was slight from 40 to 70 years, but more pronounced after age 70. Both FSH and LH were significantly correlated with age (r = 0.320, p
groups. Total Testosterone. Serum testosterone results are shown in Figure 1. Mean serum levels (Table I) did not change until after the 7th decade. After age 70
there was a significant linear (r = -0.228, p
, 04zb
3b
40
50
60
70
80
90
100
AGE (YEARS)
Figure 2. Free testosterone-index values in men 18 to 97 years of age. The dotted line indicates the lower limit of normal for men less than 45 years of age. (See text for derivation of index values.)
November 1974
The American Journal of Medicine
Volume 57
763
TESTICULAR
FUNCTION AND AGING-STEARNS
ET AL.
(SD) cm in 116 men over 60 years of age. This compares to a mean length of 5.1 f 0.5 (SD) cm in a group of 46 subjects aged 16 to 25 from a previous study [25]. The mean testis length in 90 of the old men (78 per cent) was 4.0 cm or less, the reported lower limit of normal for young adults [26]. Mean testicular volume was 17.1 f 4.0 (SD) ml, as compared to Prader’s [ 151 finding of a testis volume of 15 to 25 ml in normal young adults. In 43 (37 per cent) of the elderly subjects the mean testis volume was 15 ml or less. There was a significant correlation between OJffi
I
M
30
40
M
60
70
80
w
100
AGE (YEARS)
Figure 3. Serum LH levels in men 18 to 97years of age. Dotted line indicates the upper limit of normal for men less than 45 years of age. 30 pg/iOO ml in 57 per cent, the upper limits of normal for young men. In many of these subjects LH and FSH levels were in the castrate range (LH >15 pgl 100 ml, FSH >lOO pug/100 ml). Discriminant Function Analysis. Since changes in total testosterone, per cent free testosterone, free testosterone-index and gonadotropin levels were observed with age, an attempt was made to determine at which age these variables could be used to best separate the subjects into “young” and “old” groups. By multiple-discriminant analysis [24] the determined age was found to be 45 to 50 years. Estradiol. Mean serum levels of estradiol (Table I) in the subjects over 60 years of age showed no significant change with age. Estradiol values were all within the normal range (1 to 4 ng/ 100 ml) for young adults [20]. The levels did correlate (p
8 i .
t
l
..
. .
o*/ 20 I
30
40
xl
60
70
80
90
loo
testicular length and volume (r = 0.749, p
Prostate Size.
Of 138 men over 60 years of age, 101 (73 per cent) were considered to have enlarged prostate glands. Those with enlarged prostate glands had significantly lower mean LH (p <0.05) and FSH (p
COMMENTS
AGE (YEARS)
Figure 4. Serum FSH levels in men. 18 to 97 years of age. Dotted line indicates the upper limit of normal for men less than 45 years of age.
764
November 1974
The American Journal of Medicine
It is evident that testicular androgenic function, as assessed by either serum total or free testosterone levels, is diminished in elderly men. The diminution first
Volume 57
FUNCTION AND AGING-STEARNS
TESTICULAR
becomes
apparent
between
the ages
ET AL.
of 45 and 50
years, and presumably reflects a reduction in the testosterone production rate [3,5,27]. A concomitant reduction in the metabolic clearance rate of testosterone with advancing age [3-51 probably explains why serum testosterone concentrations are still normal in the majority of elderly subjects. The associated elevation in serum gonadotropin levels after age 40 suggests that the reduction in androgen secretion is due to Leydig cell dysfunction and not to pituitary hypofunction. Further evidence for this contention is the diminished testosterone and estradiol response to human chorionic gonadotropin stim-
20
-Ei 8
2 3
0 0 20
IdO 2bo FREE TESTOSTERONE
20
60
ulation in elderly men [ 281. The exact nature of the gonadal secretion product responsible for the feedback regulation of gonadotropin secretion in males is as yet unclear. The observation that LH and FSH levels correlated (inversely) sig-
INDE:I(
,0.267
nificantly better with the free testosterone fraction than with the serum total testosterone concentration suggests that the free fraction may be physiologically more closely involved in feedback inhibition. Although serum estradiol levels did not show the same inverse correlation with serum gonadotropin levels, it is still possible that intracellular estradiol is an important mediator of this effect following aromatization of androgens at the hypothalamic level [ 291. The elevated FSH levels of the elderly may also be related to diminished spermatogenesis, since it appears likely that some product(s) of the germinal epithelium play a role in inhibiting FSH secretion 130,311. Although we did not examine spermatogenic function, the findings of a diminution in testicular size and negative correlations between testicular size and gonadotropin levels lends support to such a relationship, since the bulk of testicular volume is accounted for by germinal elements. There is also histologic evidence of thinning of the germinal epitheliurn in senescence [8,32] and diminished spermatozoon concentrations in the ejaculates of some elderly men [33,34]. The reduction in testicular size with aging found in the present study is at variance with the data of Lubs [ 141 who reported no change with age; however, no comparison with younger subjects was made in the latter study. In conclusion, a diminution in testicular hormone secretion appears to be a normal part of the aging process. Small testes (by young adult standards) and diminished body hair are clearly not uncommon in the elderly and therefore by inference not “abnormal.” However, the presence of very small testes together with a small prostate gland may suggest a more pathologic degree of hypogonadism. Similarly, although there is clearly a decline in Leydig cell function with age, this does not necessarily imply deleteri-
SERUM
TESTOSTERONE
(ng/lO~Oml)
Figure 5. Serum LH levels versus free resrosreroneindex and serum testosterone levels (Absckae on SemiLogarithmic Scale).
ous effects on sexual function or a “male climacteric.” In fact, there is evidence to suggest that provided general health is good, libido and potency may be well maintained in elderly men [ 351. Lastly, the presence of a low serum testosterone level without an associated elevation of gonadotropin levels should make one suspect the possibility of an hypothalamopituitary lesion, an abnormal endogenous or exogenous source of estrogen, or a circulating androgen other than testosterone. ACKNOWLEDGMENT We would like to thank Dr. F. S. Chebib for statistical advice, and Mrs. E. Dudeck, Mrs. R. Poturnak, Mr. I. Riyaz and Mrs. C. Lindsay for excellent technical assistance. The LER-907 human pituitary gonadotropin standard was a gift of the National Pituitary Agency.
ADDENDUM Since submission of this manuscript, two papers [36,37] have been published showing hormone data similar to those reported herein.
November 1974
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Volume 57
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TESTICULAR FUNCTlON AND AGING-STEARNS ET AL.
REFERENCES 1.
2.
Gandy MH, Peterson RE: Measurement of testosterone and 17-ketosteroids in plasma by the double isotope dilution derivative technique. J Clin Endocrinol Metab 28: 949, 1968. Cpppage WS, Cooner AE: Testosterone in human plasma. N Engl J Med 273: 902, 1965.
19.
20.
3.
Kent JR, Acone AB: Plasma testosterone levels and aging in males. Androgens in Normal and Pathological Conditions (Vermeulen A, Exley D, eds), Amsterdam, Excerpta Medica Foundation ICS 101: 31, 1966. 4. Vermeulen A, Rubens R, Verdonck L: Testosterone secretion and metabolism in male senescence. J Clin Endocrinol Metab 34: 730, 1972. 5. Per;ky H, Smith KD, Basu GK: Relation of psychologic measures of aggression and hostility to testosterone production in man. Psychosom Med 33: 265, 197 I. 6. Vermeulen A, Stoica T, Verdonck L: The apparent free testosterone concentration, an index of androgenicity. J Clin Endocrinol Metab 33: 759, 1971. 7. Vermeulen A: Urinary excretion of testosterone. Androgens in Normal and Pathological Conditions (Vermeulen A, Exley D, eds), Amsterdam, Excerpta Medica Foundation ICS 101: 71. 1966. 0. Bishop MWH: Aging and reproduction in the male. J Reprod Fert (suppl) 12: 65, 1970. 9. Christiansen P: Urinary follicle stimulating hormone and luteiniring hormone in normal adult men. Acta Endocrinol 71: I, 1972. 10. Ryan RJ, Faiman C: Radioimmunoassay of FSH and LH in human serum, the effects of age, and infusion of several polyamines. Gonadotropins (Rosemberg E, ed), Los Altos, Geron-X Inc., 1968. p 333. 11. Williams RH: Textbook of Endocrinology, 4th ed. Philadelphia, W. B. Saunders Co., 1968. 12. Schonfeld WA: Primary and secondary sexual characteristics. Study of their development in males from birth through maturity, with biometric study of penis and testis. Am J Dis Child 65: 535, 1943. 13. Wells LJ: Descent of the testis: anatomical and hormonal considerations. Recent Adv Surg 436, 1943. 14. Lubs HA: Testicular size in Klinefelter’s syndrome in men over fifty. N Engl J Med 267: 326, 1972. 15. Prader A: Testicular size: assessment and clinical importance. Triangle 7: 240. 1966. 16. Faiman C. Ryan RJ: Radioimmunoassay for human follicle stimulating hormone. J Clin Endocrinol Metab 27: 444, 1967. 17. Falman C, Ryan RJ: Radioimmunoassay for human luteinizing hormone. Proc Sot Exp Biol Med 125: 1130, 1967. 18.
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Reyes FI, Boroditsky RS, Winter JSD, Faiman C: Studies on human sexual development. II. Fetal and maternal serum gonadotropin and sex steroid concentrations. J Clin Endocrinol Metab 36: 612, 1974.
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21. 22. 23.
24. 25. 26.
27.
28.
29.
30. 31.
32.
33.
34. 35. 36.
37.
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Rosenfield RL: Plasma testosterone binding globulin and indexes of the concentration of unbound plasma androgens in normal and hirsute subjects. J Clin Endocrinol Metab 32: 717, 1971. Winter JSD. Taraska S, Faiman C: The hormonal response to HCG stimulation in male children and adolescents. J Clin Endocrinol Metab 34: 346, 1972. Steel RGD, Torrie JH: Principles and Procedures of Statistics, New York, McGraw-Hill Inc., 1960. Ostle 6: Statistics in Research, Ames, Iowa, Iowa State College Press, 1956. p 174. Burckhardt D, Vera CA, LaDue JS: Effect of digitalis on urinary pituitary gonadotropin excretion. Ann Intern Med 66: 1069. 1968. Rao CR: Advanced Statistical Methods in Biometric Research, New York, John Wiley & Sons, 1952, p 258. Winter JSD, Faiman C: Pituitary-gonadal relations in male children and adolescents. Pediatr Res 6: 126, 1972. Greulich WW. Dorfman RI. Catchpole HR, Solomon CL, Culotta CS: Somatic and endocrine studies of pubertal and adolescent boys. Monogr Sot Res Child Dev 7, no. 3, 1942. Lipsett MD: Steroid secretion by the human testis. The Human Testis (Rosemberg E, Paulsen CA, eds), New York, Plenum Press, 1970, p 407. Longcope C: The effect of human chorionic gonadotropin on plasma steroid levels in young and old men. Steroids 21: 583, 1973. Naftolin F, Ryan KJ, Petro Z: Aromatization of androstenedione by the anterior hypothalamus of adult male and female rats. Endocrinology 90: 295, 1972. Ddell WD, Moyer DL: Physiology of Reproduction, St. Louis, C. V. Mosby Co., 1971, p 82. Leonard JM. Leach RB, Couture M, Paulsen CA: Plasma and urinary follicle stimulating hormone levels in oligospermia. J Clin Endocrinol Metab 34: 209, 1972. Albert A, Underdahl LO, Greene LR, Lorenz N: Male hypcgonadism. I. The normal testes. Mayo Clin Proc 28: 409, 1953. MacLeod J, Gold RZ: The male factor in fertility and infertility. VII. Semen quality and relation to age and sexual activity. Fertil Steril 4: 194, 1953. Andrew W: The Anatomy of Aging in Man and Animals, New York, Grune & Stratton, 1971, p 183. Masters WH, Johnson VE: Human Sexual Inadequacy, Boston, Little, Brown & Co., 1970, p 316. Rubens R, Dhont, M, Vermeulen A: Further studies on Leydig cell function in old age. J Clin Endocrinol Metab 39: 40, 1974. Pirke KM, Daerr P: Age-related changes and interrelationships between plasma testosterone, oestradiol, and testosterone-estradiol binding globulin in normal adult males. Acta Endocrinol (Kbh) 74: 792, 1973.
E. L. STEARNS,
M.Sc.
J. A. MacDONNELL,
M.D.
B. J. KAUFMAN, M.D. R. PADUA, M.D. T. S. LUCMAN, M.D. J. S. D. WINTER, M.D.’ C. FAIMAN,
M.D.’
Winnipeg, Manitoba, Canada
From the Departments of Physiology, Medicine (Geriatric Teaching Unit) and Paediatrics, University of Manitoba and the Endocrine-Metabolic Laboratory, Health Sciences Centre, Winnipeg, Manitoba, Canada. This study was supported by Research Grant 22-27-72 Deer Lodge Hospital, Department of Veterans Affairs, and M.R.C. Canada Grant MA-2997. It was presented in part at the Fifty-Fifth Meeting of the Endocrine Society, Chicago, Illinois, June 20, 1973; Gerontological Society Meeting, Houston, Texas, October 27, 1971; and the British Geriatric Society, Aberdeen, Scotland, April 12, 1973. Requests for reprints should be addressed to Dr. E. L. Stearns, G449, Health Sciences Centre, 700 William Avenue, Winnipeg, Manitoba, Canada R3E uZ3. Manuscript accepted February 15. 1974. * Queen Elizabeth II Scientist. 1 M.R.C. Canada Scholar.
Testicular endocrine function and androgen-dependent secondary Sexual characteristics were assessed in 283 men 16 to 96 years Of age. Mean serum total testosterone levels remained unchanged up to age 70 and declined thereafter. In 29 per cent of the men over 70 years of age total testosterone levels were below the lower limit of normal for young adults. In contrast, mean free or unbound testosterone levels declined after age 50 and were below the lower limit of normal for young adults in 40 per cent of the men over 70 years of age. Serum-luteinizing hormone and follicle-stimulating hormone levels showed a slight but steady rise after age 40 which became more abrupt after age 70. Serum gonadotropin levels were elevated in approximately 60 per cent of the men over 70 years of age. Mean testis length and volume were decreased in 76 per cent and 37 per cent, respectively, of the men over 60 years of age. Facial, pubic and axillary hair were also reduced in amount whereas the prostate was enlarged in 73 per cent of the elderly men. There appeared to be an inverse relationship in older men between testicular size and gonadotropin levels, and a direct relationship between testicular and prostatic sizes. It would appear that some degree of Leydig cell hypofunction commonly begins at around 45 to 50 years of age, becoming more pronounced after age 70. The concomitant elevation in serum gonadotropin levels at this time indicates that this is due to a primary decline in testicular function and is not secondary to pituitary hypofunction. The possibility of declining testicular topic for surmise and anecdote for systematic studies of this question vestigators have been unable to ences in mean serum testosterone whereas others and old men [l-3],
function with age has been a centuries, but surprisingly few have been reported. Some indemonstrate significant differconcentrations between young have reported a decline in ei-
ther serum total testosterone concentration [4,5], the free* or unbound testosterone fraction [4], or urinary excretion of testosterone glucuronide [7,8] with age. However, the observation that both serum and urinary gonadotropin levels are increased in at least some elderly men [S-10] may be evidence that declining testicular function with age is not uncommon. The clinical correlates of androgen production have been even less thoroughly studied in elderly men. Although prostatic size and
Unconjugated testosterone circulates in the blood either bound to serum proteins or in the unbound or free state. Evidence is accumulating which suggests that free testosterone is the biologically active fraction [6]. l
November 1974
The American Journal of Medicine
Volume 57
761
TESTICULAR FUNCTION AND AGING-STEARNS
ET AL.
the amount of facial and body hair are sensitive markers of the presence of androgens at puberty [ 11,12], the relationship between secondary sex characteristics and androgen concentrations in senescence are as yet undefined. Although there is his-
tologic evidence of degenerative changes in the aging testis [8], it appears that testicular weight and length do not change with age [ 13,141. The aims of our study were threefold: (1) to assess the relationship between androgenic function and aging by comparing total and free circulating testosterone levels in representative populations of old and young men; (2) to determine serum gonadotropin levels in these men in order to assess whether the suspected decline in testicular function is primarily testicular in origin or secondary to hypothalamo-pituitary hypofunction; and (3) to provide clinical data on testicular size and androgen-dependent sexual characteristics, correlating any changes in these features with hormonal alterations. MATERIALS
AND METHODS
Subjects. Two hundred eighty-three men aged 18 to 96 were studied. Of these, 142 were over the age of 60 and were drawn from the Geriatric Teaching Unit at Deer Lodge (Veterans) Hospital; the remaining 14 1 were healthy hospital personnel and Red Cross blood donors. For inclusion in the study each of the subjects over 60 years of age had no history of alcoholism, a physical examination within normal limits for his age, a normal urinalysis, a blood urea nitrogen level below 40 mg/lOO ml and a hemoglobin level above 11 g/100 ml. Forty of these men were taking occasional sedatives, 14 were taking digitalis, and 19 were taking both sedatives and digitalis. The men under 60 years of age were in good health and were not taking any medication at the time of study; they were not given a physical examination. Testicular Size and Secondary Sexual Characteristics. All measurements were obtained by at least two observers. When observations differed and the subject could not be reexamined, the disputed data were not used. In addition, some subjects refused either the clinical or the endocrine assessment. Testicular size was determined in 116 men both by measuring testicular length (mean of longest diameter of both sides in centimeters) with a rule and by estimating the mean testicular volume using the Prader orchidometer [ 151. Facial, axillary and pubic hair in 140 men was either normal or decreased in amount. Prostate size in 138 men was recorded as either normal or enlarged. Blood Samples. Twenty milliliter samples of blood were taken by venipuncture between 0800 and 1100 hours, allowed to clot and the serums frozen at -2O’C. All assays were carried out in duplicate. Gonadotropins. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were measured by radioimmunoassay [ 16,171. Levels are expressed in terms of the pituitary standard LER-907. Total Testosterone. Serum testosterone levels were
INovember 1974
The American Journal of Medicine
Volume 57
TESTICULAR
measured by radioimmunoassay [ 181 without column or thin layer chromatography, steps which were found not to be necessary for nonpregnant serum estimations. Per Cent Free Testosterone. The per cent free testosterone was measured by a modification of the method of Rosenfield [ 191; 1 ml 0.1 per cent charcoal 0.01 per cent dextran-80 (Pharmacia) suspension was used to separate bound from free testosterone. The intra-assay coefficient of variance between duplicates was f2.5 per cent, and the interassay coefficient of variance was f3 per cent. Correction for interassay variation was found to be unnecessary. Free Testosterone-Index. The free testosterone-index was calculated by multiplying the per cent free testosterone by the total testosterone concentration for each subject. Although determined under in vitro conditions, the index provides an estimate of the unbound testosterone concentration in vivo. Estradiol. Serum estradiol levels 1201 were measured by radioimmunoassay in 93 subjects over 60 years of age. Linear and log-linear correlations Statistical Analysis. [21,22] were determined among the variables of age, FSH, LH, total testosterone, per cent free testosterone, free testosterone-index, estradiol and testicular size. Each of these variables was also compared with the clinical variables in the subjects over age 60 years. The hormone levels of each of the clinical groups (those with normal or increased prostate size; those with normal or decreased sexual hair) were compared by an unpaired t test [ 2 l] Relationships among the clinical variables were assessed by Chi-square analysis [ 2 l] RESULTS In order to rule Effects of Digitalis and Sedatives. out a possible effect of digitalis, which may have estrogenic properties [23], or of sedatives on the variables studied, subjects taking one or both types of drugs were compared with their untreated peers. There were no significant differences among the
FUNCTION AND AGING-STEARNS
ET AL.
AGE (YEARS)
Figure 1. Serum total testosterone levels in men 18 to 97 years of age. The doffed line indicates the lower limit of normal for men less than 45 years of age.
age 50 (as opposed to age 70 for total testosterone) as a consequence of the decline in per cent free testosterone (Table I); and (2) 40 per cent ‘of the men over 70 years of age had free testosterone-index levels below 100, the lower limit of normal for young men. Gonadotropins. Mean serum LH and FSH levels (Figures 3 and 4, respectively and Table I) remained constant until age 40 at which time they began to rise. The rise was slight from 40 to 70 years, but more pronounced after age 70. Both FSH and LH were significantly correlated with age (r = 0.320, p
groups. Total Testosterone. Serum testosterone results are shown in Figure 1. Mean serum levels (Table I) did not change until after the 7th decade. After age 70
there was a significant linear (r = -0.228, p
, 04zb
3b
40
50
60
70
80
90
100
AGE (YEARS)
Figure 2. Free testosterone-index values in men 18 to 97 years of age. The dotted line indicates the lower limit of normal for men less than 45 years of age. (See text for derivation of index values.)
November 1974
The American Journal of Medicine
Volume 57
763
TESTICULAR
FUNCTION AND AGING-STEARNS
ET AL.
(SD) cm in 116 men over 60 years of age. This compares to a mean length of 5.1 f 0.5 (SD) cm in a group of 46 subjects aged 16 to 25 from a previous study [25]. The mean testis length in 90 of the old men (78 per cent) was 4.0 cm or less, the reported lower limit of normal for young adults [26]. Mean testicular volume was 17.1 f 4.0 (SD) ml, as compared to Prader’s [ 151 finding of a testis volume of 15 to 25 ml in normal young adults. In 43 (37 per cent) of the elderly subjects the mean testis volume was 15 ml or less. There was a significant correlation between OJffi
I
M
30
40
M
60
70
80
w
100
AGE (YEARS)
Figure 3. Serum LH levels in men 18 to 97years of age. Dotted line indicates the upper limit of normal for men less than 45 years of age. 30 pg/iOO ml in 57 per cent, the upper limits of normal for young men. In many of these subjects LH and FSH levels were in the castrate range (LH >15 pgl 100 ml, FSH >lOO pug/100 ml). Discriminant Function Analysis. Since changes in total testosterone, per cent free testosterone, free testosterone-index and gonadotropin levels were observed with age, an attempt was made to determine at which age these variables could be used to best separate the subjects into “young” and “old” groups. By multiple-discriminant analysis [24] the determined age was found to be 45 to 50 years. Estradiol. Mean serum levels of estradiol (Table I) in the subjects over 60 years of age showed no significant change with age. Estradiol values were all within the normal range (1 to 4 ng/ 100 ml) for young adults [20]. The levels did correlate (p
8 i .
t
l
..
. .
o*/ 20 I
30
40
xl
60
70
80
90
loo
testicular length and volume (r = 0.749, p
Prostate Size.
Of 138 men over 60 years of age, 101 (73 per cent) were considered to have enlarged prostate glands. Those with enlarged prostate glands had significantly lower mean LH (p <0.05) and FSH (p
COMMENTS
AGE (YEARS)
Figure 4. Serum FSH levels in men. 18 to 97 years of age. Dotted line indicates the upper limit of normal for men less than 45 years of age.
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It is evident that testicular androgenic function, as assessed by either serum total or free testosterone levels, is diminished in elderly men. The diminution first
Volume 57
FUNCTION AND AGING-STEARNS
TESTICULAR
becomes
apparent
between
the ages
ET AL.
of 45 and 50
years, and presumably reflects a reduction in the testosterone production rate [3,5,27]. A concomitant reduction in the metabolic clearance rate of testosterone with advancing age [3-51 probably explains why serum testosterone concentrations are still normal in the majority of elderly subjects. The associated elevation in serum gonadotropin levels after age 40 suggests that the reduction in androgen secretion is due to Leydig cell dysfunction and not to pituitary hypofunction. Further evidence for this contention is the diminished testosterone and estradiol response to human chorionic gonadotropin stim-
20
-Ei 8
2 3
0 0 20
IdO 2bo FREE TESTOSTERONE
20
60
ulation in elderly men [ 281. The exact nature of the gonadal secretion product responsible for the feedback regulation of gonadotropin secretion in males is as yet unclear. The observation that LH and FSH levels correlated (inversely) sig-
INDE:I(
,0.267
nificantly better with the free testosterone fraction than with the serum total testosterone concentration suggests that the free fraction may be physiologically more closely involved in feedback inhibition. Although serum estradiol levels did not show the same inverse correlation with serum gonadotropin levels, it is still possible that intracellular estradiol is an important mediator of this effect following aromatization of androgens at the hypothalamic level [ 291. The elevated FSH levels of the elderly may also be related to diminished spermatogenesis, since it appears likely that some product(s) of the germinal epithelium play a role in inhibiting FSH secretion 130,311. Although we did not examine spermatogenic function, the findings of a diminution in testicular size and negative correlations between testicular size and gonadotropin levels lends support to such a relationship, since the bulk of testicular volume is accounted for by germinal elements. There is also histologic evidence of thinning of the germinal epitheliurn in senescence [8,32] and diminished spermatozoon concentrations in the ejaculates of some elderly men [33,34]. The reduction in testicular size with aging found in the present study is at variance with the data of Lubs [ 141 who reported no change with age; however, no comparison with younger subjects was made in the latter study. In conclusion, a diminution in testicular hormone secretion appears to be a normal part of the aging process. Small testes (by young adult standards) and diminished body hair are clearly not uncommon in the elderly and therefore by inference not “abnormal.” However, the presence of very small testes together with a small prostate gland may suggest a more pathologic degree of hypogonadism. Similarly, although there is clearly a decline in Leydig cell function with age, this does not necessarily imply deleteri-
SERUM
TESTOSTERONE
(ng/lO~Oml)
Figure 5. Serum LH levels versus free resrosreroneindex and serum testosterone levels (Absckae on SemiLogarithmic Scale).
ous effects on sexual function or a “male climacteric.” In fact, there is evidence to suggest that provided general health is good, libido and potency may be well maintained in elderly men [ 351. Lastly, the presence of a low serum testosterone level without an associated elevation of gonadotropin levels should make one suspect the possibility of an hypothalamopituitary lesion, an abnormal endogenous or exogenous source of estrogen, or a circulating androgen other than testosterone. ACKNOWLEDGMENT We would like to thank Dr. F. S. Chebib for statistical advice, and Mrs. E. Dudeck, Mrs. R. Poturnak, Mr. I. Riyaz and Mrs. C. Lindsay for excellent technical assistance. The LER-907 human pituitary gonadotropin standard was a gift of the National Pituitary Agency.
ADDENDUM Since submission of this manuscript, two papers [36,37] have been published showing hormone data similar to those reported herein.
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TESTICULAR FUNCTlON AND AGING-STEARNS ET AL.
REFERENCES 1.
2.
Gandy MH, Peterson RE: Measurement of testosterone and 17-ketosteroids in plasma by the double isotope dilution derivative technique. J Clin Endocrinol Metab 28: 949, 1968. Cpppage WS, Cooner AE: Testosterone in human plasma. N Engl J Med 273: 902, 1965.
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Kent JR, Acone AB: Plasma testosterone levels and aging in males. Androgens in Normal and Pathological Conditions (Vermeulen A, Exley D, eds), Amsterdam, Excerpta Medica Foundation ICS 101: 31, 1966. 4. Vermeulen A, Rubens R, Verdonck L: Testosterone secretion and metabolism in male senescence. J Clin Endocrinol Metab 34: 730, 1972. 5. Per;ky H, Smith KD, Basu GK: Relation of psychologic measures of aggression and hostility to testosterone production in man. Psychosom Med 33: 265, 197 I. 6. Vermeulen A, Stoica T, Verdonck L: The apparent free testosterone concentration, an index of androgenicity. J Clin Endocrinol Metab 33: 759, 1971. 7. Vermeulen A: Urinary excretion of testosterone. Androgens in Normal and Pathological Conditions (Vermeulen A, Exley D, eds), Amsterdam, Excerpta Medica Foundation ICS 101: 71. 1966. 0. Bishop MWH: Aging and reproduction in the male. J Reprod Fert (suppl) 12: 65, 1970. 9. Christiansen P: Urinary follicle stimulating hormone and luteiniring hormone in normal adult men. Acta Endocrinol 71: I, 1972. 10. Ryan RJ, Faiman C: Radioimmunoassay of FSH and LH in human serum, the effects of age, and infusion of several polyamines. Gonadotropins (Rosemberg E, ed), Los Altos, Geron-X Inc., 1968. p 333. 11. Williams RH: Textbook of Endocrinology, 4th ed. Philadelphia, W. B. Saunders Co., 1968. 12. Schonfeld WA: Primary and secondary sexual characteristics. Study of their development in males from birth through maturity, with biometric study of penis and testis. Am J Dis Child 65: 535, 1943. 13. Wells LJ: Descent of the testis: anatomical and hormonal considerations. Recent Adv Surg 436, 1943. 14. Lubs HA: Testicular size in Klinefelter’s syndrome in men over fifty. N Engl J Med 267: 326, 1972. 15. Prader A: Testicular size: assessment and clinical importance. Triangle 7: 240. 1966. 16. Faiman C. Ryan RJ: Radioimmunoassay for human follicle stimulating hormone. J Clin Endocrinol Metab 27: 444, 1967. 17. Falman C, Ryan RJ: Radioimmunoassay for human luteinizing hormone. Proc Sot Exp Biol Med 125: 1130, 1967. 18.
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Rosenfield RL: Plasma testosterone binding globulin and indexes of the concentration of unbound plasma androgens in normal and hirsute subjects. J Clin Endocrinol Metab 32: 717, 1971. Winter JSD. Taraska S, Faiman C: The hormonal response to HCG stimulation in male children and adolescents. J Clin Endocrinol Metab 34: 346, 1972. Steel RGD, Torrie JH: Principles and Procedures of Statistics, New York, McGraw-Hill Inc., 1960. Ostle 6: Statistics in Research, Ames, Iowa, Iowa State College Press, 1956. p 174. Burckhardt D, Vera CA, LaDue JS: Effect of digitalis on urinary pituitary gonadotropin excretion. Ann Intern Med 66: 1069. 1968. Rao CR: Advanced Statistical Methods in Biometric Research, New York, John Wiley & Sons, 1952, p 258. Winter JSD, Faiman C: Pituitary-gonadal relations in male children and adolescents. Pediatr Res 6: 126, 1972. Greulich WW. Dorfman RI. Catchpole HR, Solomon CL, Culotta CS: Somatic and endocrine studies of pubertal and adolescent boys. Monogr Sot Res Child Dev 7, no. 3, 1942. Lipsett MD: Steroid secretion by the human testis. The Human Testis (Rosemberg E, Paulsen CA, eds), New York, Plenum Press, 1970, p 407. Longcope C: The effect of human chorionic gonadotropin on plasma steroid levels in young and old men. Steroids 21: 583, 1973. Naftolin F, Ryan KJ, Petro Z: Aromatization of androstenedione by the anterior hypothalamus of adult male and female rats. Endocrinology 90: 295, 1972. Ddell WD, Moyer DL: Physiology of Reproduction, St. Louis, C. V. Mosby Co., 1971, p 82. Leonard JM. Leach RB, Couture M, Paulsen CA: Plasma and urinary follicle stimulating hormone levels in oligospermia. J Clin Endocrinol Metab 34: 209, 1972. Albert A, Underdahl LO, Greene LR, Lorenz N: Male hypcgonadism. I. The normal testes. Mayo Clin Proc 28: 409, 1953. MacLeod J, Gold RZ: The male factor in fertility and infertility. VII. Semen quality and relation to age and sexual activity. Fertil Steril 4: 194, 1953. Andrew W: The Anatomy of Aging in Man and Animals, New York, Grune & Stratton, 1971, p 183. Masters WH, Johnson VE: Human Sexual Inadequacy, Boston, Little, Brown & Co., 1970, p 316. Rubens R, Dhont, M, Vermeulen A: Further studies on Leydig cell function in old age. J Clin Endocrinol Metab 39: 40, 1974. Pirke KM, Daerr P: Age-related changes and interrelationships between plasma testosterone, oestradiol, and testosterone-estradiol binding globulin in normal adult males. Acta Endocrinol (Kbh) 74: 792, 1973.