- Email: [email protected]
Daily Variation of Plasma Testosterone, Androstenedione, and Corticosterone in Rats under Food Restriction
Hormones and Behavior 31, 97–100 (1997) Article No. HB971321
BRIEF REPORT Daily Variation of Plasma Testosterone, Androstenedione, and Corticosterone in Rats under Food Restriction Angela M. O. Leal and Ayrton C. Moreira Division of Endocrinology, Faculty of Medicine, Ribeira˜o Preto, Brazil
Food availability is an important synchronizer of the pituitary–adrenal axis and daytime restriction of food access phase-shifts the diurnal periodicity of plasma corticosterone (B) concentration in rats. However, little is known about the synchronizers of circulating androgens in male rats. We studied intact and castrated male rats with free access to food (control groups, C) and with access to food only from 0900 to 1100 hr (food-restricted groups, FR) for 14 days. Blood samples were collected on the 15th day by decapitation at 4-hr intervals. Plasma B concentration in C groups presented diurnal variation with higher values at 2000 than at 0800 hr. In the FR groups there was a 12-hr shift of peak B values. Apparently, castration had no effect on plasma B diurnal variation. In intact rats, plasma testosterone presented similar diurnal variation in both the C and the FR groups. In castrated rats, plasma testosterone was undetectable. Plasma androstenedione similarly varied over time in both C and FR intact rats. However, in castrated animals, the diurnal variation of plasma androstenedione was abolished. Our results indicate that the daily variation of plasma testosterone and androstenedione is dependent on testicular secretion and is not influenced by food availability in the male rat. q 1997 Academic Press
able only from 0900 to 1100 hr (Krieger, 1974; Moreira and Krieger, 1982; Leal, Forsling, and Moreira, 1995). However, little is known about the effects of restricting food consumption to the morning on endocrine systems other than the pituitary – adrenal axis. Although there have been several reports on the circadian rhythms of circulating androgens in male rats (Mock, Norton, and Frankel, 1978; Heywood, 1980; Keating and Tcholakian, 1979; Kalra and Kalra, 1979), their origin is still controversial and their synchronizers have not been established. Additionally, Kalra and Kalra (1979) suggested that adrenal secretion influences the daily serum androgen periodicity. In the present study we attempted to investigate the role of food restriction on the diurnal variation of plasma testosterone and androstenedione in intact and castrated male rats, compared to pituitary – adrenal axis nycthemeral variation.
METHODS Animals and Procedures
There is a close relationship between the nutritional status of mammals, including humans, and the activity of the hypothalamic – pituitary – adrenal and gonadal axis (Grewal, Mickelsen, and Hafs, 1971; Dallman, Strack, Akana, Bradbury, Hanson, Scribner, and Smith, 1993; Perheentupa, Bergendahl, and Huhtaniemi, 1995). The effect of food restriction on basal and stress pituitary – adrenal axis activity has received a great deal of attention. It is well established that plasma corticosterone (B) levels display a 12-hr shift when food is avail-
Studies used male Wistar rats (aged 50 days, weighing 200 g) from our own colony. Animals were initially grouped randomly into castrated and intact controls. Castration was performed via the scrotal route under ether anesthesia. Animals were then housed for 10 days in individual hanging wire cages under controlled conditions of temperature, humidity, and lighting (lights on 0700 – 1900 hr), with free access to rat chow and tap water. After this acclimation period, castrated and intact rats were divided into two groups, a control group (C) with food
0018-506X/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
AID
H&B 1321
/
6805h$$$81
97
03-13-97 19:41:27
haba
AP: H & B
98
Leal and Moreira
FIG. 1. Diurnal variation of plasma B concentrations in control (closed circles) or food-restricted (open circles) intact rats (a) and in control (closed triangles) or food-restricted (open triangles) castrated rats (b). Values are means { SEM for 5 – 20 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
available at all times and a food-restricted group (FR) with access to food only from 0900 to 1100 hr for 14 days. On the 15th day, animals were sacrificed by decapitation and blood was collected at 0800, 1200, 1600, 2000, 2400, 0400, and 0800 hr. Plasma samples were frozen at 0207C for later determination of B, testosterone, and androstenedione by RIA.
intact (Fig. 1a) and castrated (Fig. 1b) rats (P õ 0.0001). Plasma B concentrations in the C groups of intact and castrated rats presented a diurnal variation from 1.3 { 0.2 and 1.0 { 0.3 mg/dl, respectively, at 0800 hr to 11.5 { 0.9 and 9.6 { 1.5 mg/dl (mean { SEM) at 2000 hr (P õ 0.01). The restricted feeding regimen resulted in a 12-hr shift of peak B values in both intact (12 { 0.8 vs 4 { 0.4 mg/dl, P õ 0.0001) and castrated (16.9 { 1.8 vs 6.7 { 0.7 mg/dl, P õ 0.005) rats. In intact animals, plasma testosterone (Fig. 2) presented a diurnal variation from 70.7 { 10.9 ng/dl at 0800 hr to 243 { 42.2 ng/dl at 1600 hr in group C (P õ 0.006) and from 46.2 { 7.2 ng/dl at 1200 hr to 258.3 { 61.6 ng/dl at 1600 hr (P õ 0.001), in group FR. Plasma testosterone was not detectable in castrated animals. Plasma androstenedione (Fig. 3) varied over time in intact animals, presenting higher values at 1600 than at 0800 hr in group C (49.2 { 3.0 vs 23.7 { 2.7 ng/dl, P õ 0.0001) and at 1600 than at 1200 hr in group FR (57.6 { 6.9 vs 22.5 { 2.5 ng/ dl, P õ 0.0001). In castrated animals, however, plasma androstenedione displayed no variation throughout the day in either group (P ú 0.3).
DISCUSSION Our results demonstrate the well-known diurnal variation of plasma B in rats which increases before the beginning of the dark activity period and peaks at 2000 hr. We also confirmed, as previously described
Hormone Assays Plasma B, testosterone, and androstenedione were determined by previously described RIAs (Lo´pez-Jime´nez, Valenc¸a, Moreira, and Antunes-Rodrigues, 1989; Leal, 1995; Vieira, Russo, Maciel, and Germek, 1981). The assay sensitivity and the intra- and interassay coefficient of variation were 0.5 mg/dl, 3 and 15.9% for B; 19.6 ng/dl, 5.6 and 17% for testosterone; and 4 ng/dl, 4 and 16% for androstenedione, respectively.
Data Analysis Data were analyzed statistically by ANOVA and the Wilcoxon Mann – Whitney test. Differences of less than 0.05 were considered significant.
RESULTS Figure 1 shows the result of plasma B determination. Plasma B varied over time in C and FR groups of both
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
FIG. 2. Diurnal variation of plasma testosterone concentrations in control (closed circles) or food-restricted (open circles) intact rats and in control (closed triangles) or food-restricted (open triangles) castrated rats. Values are means { SEM for 5 – 10 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
haba
AP: H & B
99
Food and Androgens
FIG. 3. Diurnal variation of plasma androstenedione concentrations in control (closed circles) or food-restricted (open circles) intact rats and in control (closed triangles) or food-restricted (open triangles) castrated rats. Values are means { SEM for 5 – 20 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
(Krieger, 1974; Moreira and Krieger, 1982; Leal et al., 1995), that B levels show a 12-hr shift when the food is restricted from 0900 to 1100 hr. However, castration had no effect on the pattern of plasma B diurnal variation in either group. These results partially disagree with a previous report (Critchlow, Liebelt, Bar-Sela, Mountcastle, and Lipscomb, 1963). In intact control rats, plasma testosterone presented diurnal variation with higher levels at 1600 than at 0800 hr. This pattern was similar to that described by Kalra and Kalra (1977). Although diurnal variations have been observed in adult rats, there is no consensus about peaks and nadirs in plasma testosterone during the 24hr period (Kinson and Liu, 1973; Mock, Kamel, Wright, and Frankel, 1975; Kalra and Kalra, 1977; Norton and Frankel, 1978; Keating and Tcholakian, 1979; Heywood, 1980). This variation may be related to several factors such as age, strains, housing, methods and time of sampling, and seasonal variations (Mock et al., 1975). In the present study we did not observe a shift of plasma testosterone peak parallel to that observed for plasma B in food-restricted animals. The undetectable levels of plasma testosterone in castrated animals indicate that the testes are the major site of origin of testosterone in the rat, as already shown by Kalra and Kalra (1977) and Be´langer, Be´langer, Labrie, Dupont, Cusan, and Monfette (1989). Plasma androstenedione displayed diurnal variation in both control and food-restricted intact rats. As al-
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
ready observed for plasma testosterone, the food restriction regimen was not able to modify the pattern of plasma androstenedione variation. Interestingly, castration abolished the daily variation of plasma androstenedione in both the control and the food-restricted groups. These results indicate that the diurnal variation of plasma testosterone and androstenedione in rats is dependent on testicular secretion. The mechanisms responsible for the daily rhythmicity of the gonadal axis are not yet characterized. Although the pituitary – gonadal axis has been shown to be sensitive to underfeeding (Grewal, Mickelsen, and Hafs, 1971; Negro-Vilar, Dickerman, and Meites, 1971; Howland and Skinner, 1973; Howland, 1975; Badger, Lynch, and Fox, 1985), our results originally demonstrate that the availability of food during only certain hours of the day does not seem to be as important as a synchronizing agent of the diurnal variation of the pituitary – gonadal axis as it is for the pituitary – adrenal axis. Kalra and Kalra (1979) postulated that circadian adrenal secretion causes rhythmic variations in gonadal hormone secretion. However, our data show that the diurnal variation of androgens is not dependent on the adrenal secretion of corticosterone. Probably, different mechanisms are involved in the determination of gonadal and adrenal circadian periodicities.
ACKNOWLEDGMENTS We are grateful to Mr. Adalberto Verceze, Mrs. Adriana Rossi, Mrs. Lucimara Bueno, and Mr. Jose´ Roberto Silva for technical assistance and to Mr. Alex A. da Silva for secretarial assistance. This work was supported by Conselho Nacional de Desenvolvimento CientıB fico e Tecnolo´gico, Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de NıB vel Superior, and HCFMRP-FAEPA.
REFERENCES Badger, T. M., Lynch, E. A., and Fox, P. H. (1985). Effects of fasting on luteinizing hormone dynamics in the male rat. J. Nutr. 115, 788 – 797. Be´langer, B., Be´langer, A., Labrie, F., Dupont, A., Cusan, L., and Monfette, G. (1989). Comparison of residual C-19 steroids in plasma and prostatic tissue of human, rat and guinea pig after castration: Unique importance of extratesticular androgens in men. J. Steroid Biochem. 32, 695 – 698. Critchlow, V., Liebelt, R. A., Bar-Sela, M., Mountcastle, W., and Lipscomb, H. S. (1963). Sex difference in resting pituitary – adrenal function in the rat. Am. J. Physiol. 205, 807 – 815. Dallman, M. F., Strack, A. M., Akana, S. F., Bradbury, M. J., Hanson, E. S., Scribner, K. A., and Smith, M. (1993). Feast and famine: Critical
haba
AP: H & B
100
Leal and Moreira
role of glucocorticoids with insulin in daily energy flow. Front. Neuroendocrinol. 14, 303 – 347. Grewal, T., Mickelsen, O., and Hafs, H. D. (1971). Androgen secretion and spermatogenesis in rats following semistarvation. Proc. Soc. Exp. Biol. Med. 138, 723 – 727. Heywood, L. H. (1980). Testosterone levels in the male laboratory rat: Variation under experimental conditions. Int. J. Androl. 3, 519 – 529. Howland, B. E., and Skinner, K. R. (1973). Effect of starvation on gonadotropin secretion in intact and castrated male rats. Can. J. Physiol. Pharmacol. 51, 759 – 762. Howland, B. E. (1975). Effect of short period of fasting and time of day on serum levels of gonadotropins, testosterone and glucose in male rats. Horm. Metab. Res. 7, 40 – 43. Kalra, P. S., and Kalra, S. P. (1977). Circadian periodicities of serum androgens, progesterone, gonadotropins and luteinizing hormonereleasing hormone in male rats: The effects of hypothalamic deafferentation, castration and adrenalectomy. Endocrinology 101, 1821 – 1827. Kalra, P. S., and Kalra, S. P. (1979). Regulation of gonadal steroid rhythms in rats. J. Steroid Biochem. 11, 981 – 987. Keating, R. J., and Tcholakian, R. K. (1979). In vivo patterns of circulating steroids in adult male rats. Variations in testosterone during 24- and 48-hour standard and reverse light/dark cycles. Endocrinology 104, 184 – 188. Kinson, G. A., and Liu, C. (1973). Diurnal variation in plasma testosterone of the male laboratory rat. Horm. Metab. Res. 5, 233 – 234. Krieger, D. T. (1974). Food and water restriction shifts corticosterone, temperature, activity and brain amine periodicity. Endocrinology 95, 1195 – 1201. Leal, A. M. O., Forsling, M. L., and Moreira, A. C. (1995). Diurnal
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
variation of the pituitary – adrenal and AVP responses to stress in rats under food restriction. Life Sci. 56, 191 – 198. Leal, A. M. O. (1995). Variac¸a˜o diurna do eixo hipota´lamo-hipo´fiseadrenal e andro´genos no rato sob restric¸a˜o alimentar. Thesis. Ribeira˜o Preto, 1 – 172. Lo´pez, Jimenez, M., Valenc¸a, M. M., Moreira, A. C., and AntunesRodrigues, J. (1989). Ether and immobilization stress effects on pituitary-adrenal function in hemidecorticated rats. Braz. J. Med. Biol. Res. 22, 779 – 782. Mock, E. J., Kamel, F., Wright, W. W., and Frankel, A. J. (1975). Seasonal rhythm in plasma testosterone and luteinising hormone of the male laboratory rat. Nature 256, 61 – 63. Mock, E. J., Norton, H. W., and Frankel, A. I. (1978). Daily rhythmicity of serum testosterone concentration in the male laboratory rat. Endocrinology 103, 1111 – 1121. Moreira, A. C., and Krieger, D. T. (1982). The effects of subdiaphragmatic vagotomy on circadian corticosterone rhythmicity in rats with continuous or restricted food access. Physiol. Behav. 28, 787 – 790. Negro-Vilar, A., Dickerman, E., and Meites, J. (1971). Effects of starvation on hypothalamic FSH-RF and pituitary FSH in male rats. Endocrinology 88, 1246 – 1249. Perheentupa, A., Bergendahl, M., and Huhtaniemi, I. (1995). Modulation of gonadatropin secretion at the pituitary level by testosterone in gonadotropin-releasing hormone-treated males rats during food deprivation. Biol. Reprod. 52, 808 – 813. Vieira, J. G. H., Russo, E. M. K., Maciel, R. M. B., and Germek, O. A. (1981). Desenrolvimento de um me´todo radioimunolo´gico simples para dosagem de androstenediona no soro. Arq. Bras. Endocrinol. Metab. 25, 47 – 50.
haba
AP: H & B
BRIEF REPORT Daily Variation of Plasma Testosterone, Androstenedione, and Corticosterone in Rats under Food Restriction Angela M. O. Leal and Ayrton C. Moreira Division of Endocrinology, Faculty of Medicine, Ribeira˜o Preto, Brazil
Food availability is an important synchronizer of the pituitary–adrenal axis and daytime restriction of food access phase-shifts the diurnal periodicity of plasma corticosterone (B) concentration in rats. However, little is known about the synchronizers of circulating androgens in male rats. We studied intact and castrated male rats with free access to food (control groups, C) and with access to food only from 0900 to 1100 hr (food-restricted groups, FR) for 14 days. Blood samples were collected on the 15th day by decapitation at 4-hr intervals. Plasma B concentration in C groups presented diurnal variation with higher values at 2000 than at 0800 hr. In the FR groups there was a 12-hr shift of peak B values. Apparently, castration had no effect on plasma B diurnal variation. In intact rats, plasma testosterone presented similar diurnal variation in both the C and the FR groups. In castrated rats, plasma testosterone was undetectable. Plasma androstenedione similarly varied over time in both C and FR intact rats. However, in castrated animals, the diurnal variation of plasma androstenedione was abolished. Our results indicate that the daily variation of plasma testosterone and androstenedione is dependent on testicular secretion and is not influenced by food availability in the male rat. q 1997 Academic Press
able only from 0900 to 1100 hr (Krieger, 1974; Moreira and Krieger, 1982; Leal, Forsling, and Moreira, 1995). However, little is known about the effects of restricting food consumption to the morning on endocrine systems other than the pituitary – adrenal axis. Although there have been several reports on the circadian rhythms of circulating androgens in male rats (Mock, Norton, and Frankel, 1978; Heywood, 1980; Keating and Tcholakian, 1979; Kalra and Kalra, 1979), their origin is still controversial and their synchronizers have not been established. Additionally, Kalra and Kalra (1979) suggested that adrenal secretion influences the daily serum androgen periodicity. In the present study we attempted to investigate the role of food restriction on the diurnal variation of plasma testosterone and androstenedione in intact and castrated male rats, compared to pituitary – adrenal axis nycthemeral variation.
METHODS Animals and Procedures
There is a close relationship between the nutritional status of mammals, including humans, and the activity of the hypothalamic – pituitary – adrenal and gonadal axis (Grewal, Mickelsen, and Hafs, 1971; Dallman, Strack, Akana, Bradbury, Hanson, Scribner, and Smith, 1993; Perheentupa, Bergendahl, and Huhtaniemi, 1995). The effect of food restriction on basal and stress pituitary – adrenal axis activity has received a great deal of attention. It is well established that plasma corticosterone (B) levels display a 12-hr shift when food is avail-
Studies used male Wistar rats (aged 50 days, weighing 200 g) from our own colony. Animals were initially grouped randomly into castrated and intact controls. Castration was performed via the scrotal route under ether anesthesia. Animals were then housed for 10 days in individual hanging wire cages under controlled conditions of temperature, humidity, and lighting (lights on 0700 – 1900 hr), with free access to rat chow and tap water. After this acclimation period, castrated and intact rats were divided into two groups, a control group (C) with food
0018-506X/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
AID
H&B 1321
/
6805h$$$81
97
03-13-97 19:41:27
haba
AP: H & B
98
Leal and Moreira
FIG. 1. Diurnal variation of plasma B concentrations in control (closed circles) or food-restricted (open circles) intact rats (a) and in control (closed triangles) or food-restricted (open triangles) castrated rats (b). Values are means { SEM for 5 – 20 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
available at all times and a food-restricted group (FR) with access to food only from 0900 to 1100 hr for 14 days. On the 15th day, animals were sacrificed by decapitation and blood was collected at 0800, 1200, 1600, 2000, 2400, 0400, and 0800 hr. Plasma samples were frozen at 0207C for later determination of B, testosterone, and androstenedione by RIA.
intact (Fig. 1a) and castrated (Fig. 1b) rats (P õ 0.0001). Plasma B concentrations in the C groups of intact and castrated rats presented a diurnal variation from 1.3 { 0.2 and 1.0 { 0.3 mg/dl, respectively, at 0800 hr to 11.5 { 0.9 and 9.6 { 1.5 mg/dl (mean { SEM) at 2000 hr (P õ 0.01). The restricted feeding regimen resulted in a 12-hr shift of peak B values in both intact (12 { 0.8 vs 4 { 0.4 mg/dl, P õ 0.0001) and castrated (16.9 { 1.8 vs 6.7 { 0.7 mg/dl, P õ 0.005) rats. In intact animals, plasma testosterone (Fig. 2) presented a diurnal variation from 70.7 { 10.9 ng/dl at 0800 hr to 243 { 42.2 ng/dl at 1600 hr in group C (P õ 0.006) and from 46.2 { 7.2 ng/dl at 1200 hr to 258.3 { 61.6 ng/dl at 1600 hr (P õ 0.001), in group FR. Plasma testosterone was not detectable in castrated animals. Plasma androstenedione (Fig. 3) varied over time in intact animals, presenting higher values at 1600 than at 0800 hr in group C (49.2 { 3.0 vs 23.7 { 2.7 ng/dl, P õ 0.0001) and at 1600 than at 1200 hr in group FR (57.6 { 6.9 vs 22.5 { 2.5 ng/ dl, P õ 0.0001). In castrated animals, however, plasma androstenedione displayed no variation throughout the day in either group (P ú 0.3).
DISCUSSION Our results demonstrate the well-known diurnal variation of plasma B in rats which increases before the beginning of the dark activity period and peaks at 2000 hr. We also confirmed, as previously described
Hormone Assays Plasma B, testosterone, and androstenedione were determined by previously described RIAs (Lo´pez-Jime´nez, Valenc¸a, Moreira, and Antunes-Rodrigues, 1989; Leal, 1995; Vieira, Russo, Maciel, and Germek, 1981). The assay sensitivity and the intra- and interassay coefficient of variation were 0.5 mg/dl, 3 and 15.9% for B; 19.6 ng/dl, 5.6 and 17% for testosterone; and 4 ng/dl, 4 and 16% for androstenedione, respectively.
Data Analysis Data were analyzed statistically by ANOVA and the Wilcoxon Mann – Whitney test. Differences of less than 0.05 were considered significant.
RESULTS Figure 1 shows the result of plasma B determination. Plasma B varied over time in C and FR groups of both
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
FIG. 2. Diurnal variation of plasma testosterone concentrations in control (closed circles) or food-restricted (open circles) intact rats and in control (closed triangles) or food-restricted (open triangles) castrated rats. Values are means { SEM for 5 – 10 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
haba
AP: H & B
99
Food and Androgens
FIG. 3. Diurnal variation of plasma androstenedione concentrations in control (closed circles) or food-restricted (open circles) intact rats and in control (closed triangles) or food-restricted (open triangles) castrated rats. Values are means { SEM for 5 – 20 rats. Solid bars indicate time of lights off. Striped bars indicate time of food presentation to food-restricted rats.
(Krieger, 1974; Moreira and Krieger, 1982; Leal et al., 1995), that B levels show a 12-hr shift when the food is restricted from 0900 to 1100 hr. However, castration had no effect on the pattern of plasma B diurnal variation in either group. These results partially disagree with a previous report (Critchlow, Liebelt, Bar-Sela, Mountcastle, and Lipscomb, 1963). In intact control rats, plasma testosterone presented diurnal variation with higher levels at 1600 than at 0800 hr. This pattern was similar to that described by Kalra and Kalra (1977). Although diurnal variations have been observed in adult rats, there is no consensus about peaks and nadirs in plasma testosterone during the 24hr period (Kinson and Liu, 1973; Mock, Kamel, Wright, and Frankel, 1975; Kalra and Kalra, 1977; Norton and Frankel, 1978; Keating and Tcholakian, 1979; Heywood, 1980). This variation may be related to several factors such as age, strains, housing, methods and time of sampling, and seasonal variations (Mock et al., 1975). In the present study we did not observe a shift of plasma testosterone peak parallel to that observed for plasma B in food-restricted animals. The undetectable levels of plasma testosterone in castrated animals indicate that the testes are the major site of origin of testosterone in the rat, as already shown by Kalra and Kalra (1977) and Be´langer, Be´langer, Labrie, Dupont, Cusan, and Monfette (1989). Plasma androstenedione displayed diurnal variation in both control and food-restricted intact rats. As al-
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
ready observed for plasma testosterone, the food restriction regimen was not able to modify the pattern of plasma androstenedione variation. Interestingly, castration abolished the daily variation of plasma androstenedione in both the control and the food-restricted groups. These results indicate that the diurnal variation of plasma testosterone and androstenedione in rats is dependent on testicular secretion. The mechanisms responsible for the daily rhythmicity of the gonadal axis are not yet characterized. Although the pituitary – gonadal axis has been shown to be sensitive to underfeeding (Grewal, Mickelsen, and Hafs, 1971; Negro-Vilar, Dickerman, and Meites, 1971; Howland and Skinner, 1973; Howland, 1975; Badger, Lynch, and Fox, 1985), our results originally demonstrate that the availability of food during only certain hours of the day does not seem to be as important as a synchronizing agent of the diurnal variation of the pituitary – gonadal axis as it is for the pituitary – adrenal axis. Kalra and Kalra (1979) postulated that circadian adrenal secretion causes rhythmic variations in gonadal hormone secretion. However, our data show that the diurnal variation of androgens is not dependent on the adrenal secretion of corticosterone. Probably, different mechanisms are involved in the determination of gonadal and adrenal circadian periodicities.
ACKNOWLEDGMENTS We are grateful to Mr. Adalberto Verceze, Mrs. Adriana Rossi, Mrs. Lucimara Bueno, and Mr. Jose´ Roberto Silva for technical assistance and to Mr. Alex A. da Silva for secretarial assistance. This work was supported by Conselho Nacional de Desenvolvimento CientıB fico e Tecnolo´gico, Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de NıB vel Superior, and HCFMRP-FAEPA.
REFERENCES Badger, T. M., Lynch, E. A., and Fox, P. H. (1985). Effects of fasting on luteinizing hormone dynamics in the male rat. J. Nutr. 115, 788 – 797. Be´langer, B., Be´langer, A., Labrie, F., Dupont, A., Cusan, L., and Monfette, G. (1989). Comparison of residual C-19 steroids in plasma and prostatic tissue of human, rat and guinea pig after castration: Unique importance of extratesticular androgens in men. J. Steroid Biochem. 32, 695 – 698. Critchlow, V., Liebelt, R. A., Bar-Sela, M., Mountcastle, W., and Lipscomb, H. S. (1963). Sex difference in resting pituitary – adrenal function in the rat. Am. J. Physiol. 205, 807 – 815. Dallman, M. F., Strack, A. M., Akana, S. F., Bradbury, M. J., Hanson, E. S., Scribner, K. A., and Smith, M. (1993). Feast and famine: Critical
haba
AP: H & B
100
Leal and Moreira
role of glucocorticoids with insulin in daily energy flow. Front. Neuroendocrinol. 14, 303 – 347. Grewal, T., Mickelsen, O., and Hafs, H. D. (1971). Androgen secretion and spermatogenesis in rats following semistarvation. Proc. Soc. Exp. Biol. Med. 138, 723 – 727. Heywood, L. H. (1980). Testosterone levels in the male laboratory rat: Variation under experimental conditions. Int. J. Androl. 3, 519 – 529. Howland, B. E., and Skinner, K. R. (1973). Effect of starvation on gonadotropin secretion in intact and castrated male rats. Can. J. Physiol. Pharmacol. 51, 759 – 762. Howland, B. E. (1975). Effect of short period of fasting and time of day on serum levels of gonadotropins, testosterone and glucose in male rats. Horm. Metab. Res. 7, 40 – 43. Kalra, P. S., and Kalra, S. P. (1977). Circadian periodicities of serum androgens, progesterone, gonadotropins and luteinizing hormonereleasing hormone in male rats: The effects of hypothalamic deafferentation, castration and adrenalectomy. Endocrinology 101, 1821 – 1827. Kalra, P. S., and Kalra, S. P. (1979). Regulation of gonadal steroid rhythms in rats. J. Steroid Biochem. 11, 981 – 987. Keating, R. J., and Tcholakian, R. K. (1979). In vivo patterns of circulating steroids in adult male rats. Variations in testosterone during 24- and 48-hour standard and reverse light/dark cycles. Endocrinology 104, 184 – 188. Kinson, G. A., and Liu, C. (1973). Diurnal variation in plasma testosterone of the male laboratory rat. Horm. Metab. Res. 5, 233 – 234. Krieger, D. T. (1974). Food and water restriction shifts corticosterone, temperature, activity and brain amine periodicity. Endocrinology 95, 1195 – 1201. Leal, A. M. O., Forsling, M. L., and Moreira, A. C. (1995). Diurnal
AID
H&B 1321
/
6805h$$$82
03-13-97 19:41:27
variation of the pituitary – adrenal and AVP responses to stress in rats under food restriction. Life Sci. 56, 191 – 198. Leal, A. M. O. (1995). Variac¸a˜o diurna do eixo hipota´lamo-hipo´fiseadrenal e andro´genos no rato sob restric¸a˜o alimentar. Thesis. Ribeira˜o Preto, 1 – 172. Lo´pez, Jimenez, M., Valenc¸a, M. M., Moreira, A. C., and AntunesRodrigues, J. (1989). Ether and immobilization stress effects on pituitary-adrenal function in hemidecorticated rats. Braz. J. Med. Biol. Res. 22, 779 – 782. Mock, E. J., Kamel, F., Wright, W. W., and Frankel, A. J. (1975). Seasonal rhythm in plasma testosterone and luteinising hormone of the male laboratory rat. Nature 256, 61 – 63. Mock, E. J., Norton, H. W., and Frankel, A. I. (1978). Daily rhythmicity of serum testosterone concentration in the male laboratory rat. Endocrinology 103, 1111 – 1121. Moreira, A. C., and Krieger, D. T. (1982). The effects of subdiaphragmatic vagotomy on circadian corticosterone rhythmicity in rats with continuous or restricted food access. Physiol. Behav. 28, 787 – 790. Negro-Vilar, A., Dickerman, E., and Meites, J. (1971). Effects of starvation on hypothalamic FSH-RF and pituitary FSH in male rats. Endocrinology 88, 1246 – 1249. Perheentupa, A., Bergendahl, M., and Huhtaniemi, I. (1995). Modulation of gonadatropin secretion at the pituitary level by testosterone in gonadotropin-releasing hormone-treated males rats during food deprivation. Biol. Reprod. 52, 808 – 813. Vieira, J. G. H., Russo, E. M. K., Maciel, R. M. B., and Germek, O. A. (1981). Desenrolvimento de um me´todo radioimunolo´gico simples para dosagem de androstenediona no soro. Arq. Bras. Endocrinol. Metab. 25, 47 – 50.
haba
AP: H & B