- Email: [email protected]
Chronic effect of hyperprolactinemia on blood glucose and lipid levels in mice
Life Sciences, Vol. 58, No. 14, pp. 1171-1177, 1% cbpylight 0 19% Ewvier science Inc. Printed in the USA All rights miawd oow3205/% sL5.M) t .cm
PII SO0243205(96)0007S-6
ELSEVIER
CHRONIC EFFECT OF HYPERPROLACTINEMIA
ON BLOOD
GLUCOSE AND LIPID LEVELS IN MICE Manabu Matsuda, Takao Mori, Shuji Sassa’, Shinobu Sakamoto*, Mm Kyun Park and Seiichiro Kawashima Department of Biological Sciences, Graduate School of Science, University of Tokyo, and *Department of Endocrinology, Tokyo Medical and Dental University,
Medical Research Institute, Bunkyo-ku,
Tokyo 113, Japan
(Received in final form January 31, 1996)
We studied the chronic effects of hyperprolactinemia, grafting, on
induced by ectopic pituitary
blood glucose and lipid levels in adult male mice. For one year after
pituitary grafting, we measured the blood levels of prolactin, growth hormone (GH), insulin, glucose and free fatty acid (FFA) at various intervals. The graft caused consistent hyperprolactinemia
without changes in the serum GH levels. Hypoglycemia
developed at 1 and 3 months after grafting but was not accompanied by any changes of the serum insulin levels. Thereafter, the blood glucose and strum insulin levels began to increase in the pituitary-grafted (PG) mice, and at 12 months after the operation, both levels became significantly higher in PG mice than controls. The serum FFA levels and the weight of epididymal fat bodies were significantly lower in PG mice than controls from 3-12 months after the grafting. Thus, hyperprolactinemia leads to persistent hypolipidemia
and biphasic changes in the blood glucose level.
Key Work: hyperprolactinemic mice, glucose metabolism, lipid metabolism, insulin
Lactation induces changes in the metabolism not only of mammary gland but also of other organs, and requires a coordinated adaptation of metabolism in the whole body, especially in small mammals such as mice (1-3). For example, lipogenesis increases in mammary glands, while lipolysis increases in the adipose tissue of lactating animals (4). In many mammals prolactin (PRL) plays a principal role in the control of partition and utilization of metabolic fuels during lactation (5). Some Correspondence:
Matsuda, M., Laboratory of Endocrinology,
Department of Biological Sciences,
Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. Phone:81-3-3812-2111ex.4436, Fax:81-3-3816-1965, e-mail: [email protected]
1172
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 19%
of these PRL effects are direct, and the others are thought to be indirect, according to changes in the circulating levels of insulin, tissue insulin receptors and post-receptor cvcnts (1, 6). Chronic
hyperprolactinemia
lcads to metabolic
’ diabetogenic hormone’ (7). Hyperprolactinemia due to the reduction
of glycolysis
disorders,
and PRL
is followed by hyperglycemia
in the liver (10). On the other hand,
is sometimes
called
(8, 9) which is partly PRL stimulates
the
proliferation of pancreatic islet B-cells and insulin secretion (11-13) and hyperprolactinemia induces hypoglycemia in mice (14). Thus, the effects of hypcrprolactinemia on fuel metabolism are considered to differ among experimental animals. To study the effects of chronic hyperprolactinemia on fuel metabolism in mice, we investigated blood glucose and free fatty acid (FFA) levels after cctopic pituitary grafting, with special reference to insulin levels. Methods Animals.
Male mice of the SHN strain (15) were housed in plastic cages with wood shavings
under controlled temperature (25 2 0.5 “C) and light (12 h of light from 6:00 to 18:OO). They were given a commercial diet (CE-7, CLEA Japan, Inc., Tokyo) and tap water ad libitum. All procedures used on the mice were described in detail in a protocol that was approved by the Animal Care and USC Committee of the Graduate School of Sdcncc, University of Tokyo. Mice were divided sham-operated
into a hyperprolactincmic
group bearing pituitary grafts (PG mice) and a
group (control mice). In PG mice, an anterior pituitary gland obtained from female
litter-mates was grafted under the left kidney capsule at 2 months of age
Both groups of mice were
weighed and killed between 13:00 and 14:00 at 0.5, 1, 3, 6, 9, 12 months after the grafting. Control mice were also killed at comparable ages. Blood samples were collected from the trunk for measuring circulating levels of glucose, FFA, growth hormone (GH), PRL, testosterone and insulin. The liver and epididymal fat body were weighed. The fat body was fixed in Bouin’s solution and prepared as 4-pm paraffin sections for hematoxylin-eosin (HE) staining. In addition, food intake was measured by the difference between the initial and final weights of food baskets for 5 days before sacrifice. Glucose. FFA and hormone determination. levels were determined
Blood glucose and serum FFA, PRL, GH and insulin
as described (16). Briefly, the blood glucose level was determined by the
glucose oxidase method (17) (Scrapaper; Eiken, Tokyo). Serum FFA lcvcl was determined using acyl-CoA synthetase and acyl-CoA oxidase reaction (18) (NEFA C-test; Wako, Tokyo). Serum PRL levels were determined by means of a homologous RIA using kit donated by Dr. A. F. Parlow (Harbor-UCLA Medical Center). Serum GH levels were measured by means of a heterologous RIA using kit donated by Dr. S. Raiti (NIDDK) and a mouse GH standard from Dr. A F. Parlow. Serum insulin levels were determined by a heterologous enzyme immunoassay (Glazyme Insulin E&Test; Wako, Tokyo). Testosterone was measured using an RIA kit (Daiichi Radioisotope Labs., Ltd., Tokyo). . . w Student’s
Differences between the means of two groups were statistically evaluated by t-test or the Cochran-Cox test, when a significant difference in variance between two
Vol. 58, No. 14, 1996
1173
Effect of PRL on Glucose and Lipid
groups was found by Bartlett’s test for the uniformity
of variance. P values of less than 5 % were
considered significant.
Results Changes in the strum PRL and GH lcvcls in PG mice are shown
PRL
in Fig. 1. In PG mice, serum PRL levels wcrc clcvated to more than ten fold those of the controls by 1 month, and the elevated lcvcl remained constant thereafter. In PG mice, there was no significant difference in the serum PRL levels was observed bctwccn 0.5 and 12 months. On the other hand, serum GH levels were little affected by the graft throughout the cxpcrimcntal period,
the level in
PG mice being esscnthally similar to that in control mice (Fig. 1).
-0
01
3
6
Months after pituitary
9
12
grafting
“01
3
6
Months after pituitary
9
12
grafting
Fig. 1 Serum prolactin (PRL) and growth hormone (GH) levels in PG mice. Vertical bars indicate the SEM (n=lO to16). There were significant differences in the strum PRL level between PG ( l ) and control ( 0 ) mice for 0.512 months after pituitary grafting. **p
. . As shown in Fig. 2, hypoglycemia was induced at 1 and 3 Glucose levels in PG ti months after the pituitary grafting. The blood glucose levels in PG mice returned to the level of control mice at 6 months,
then significantly
increased at 12 months. Serum insulin levels also were
affected by pituitary grafting. The levels decreased little at 1 and 3 months after the pituitary grafting, despite hypoglycemia. Thereafter, the insulin levels gradually increased and became significantly higher in PG mice when compared with the controls at 12 months. The body weight (BW) and that of the liver, expressed per 20 g BW, were not altered at 3 and G months after pituitary grafting, but they increased significantly between 9 and 12 months in PG mice (Table 1, data at 6 and 12 months not shown). Food intake also increased at the same time in PG mice. Serum testosterone period.
levels were not significantly
altered by the graft during the experimental
1174
Effect of PRL on Glucose and Lipid
01
3
6
9
Vol. 58, No. 14, 1996
12
Months after pituitary grafting Fig. 2 Blood glucose and serum insulin levels in PG mice. Vertical bars indicate the SEM (n=lO tol6). There were significant differences in blood glucose levels at 1, 3, and 12 months and in the serum insulin level at 12 months between PG ( l ) and control ( 0 ) mice. *p
TABLE 1 Effect of Pituitary Grafting on the Body and Liver Weight, Food Intake and Strum Testosterone
Level. 1
Months after pituitary grafting 3
9 Body weight (g) Control 26.7 c 0.3 28.1 r 0.8 28.2 r 1.0 PG 27.4 * 0.3 29.5 -e 0.6 33.R t 1.0* Weight of Iiver (g/2Og SW) Control 1.01 -f 0.03 0.99 f 0.05 1.00 * 0.03 PG 1.00 + 0.03 1.04 f 0.03 1.12 + 0.06’ Food intake (g/day/20g SW) Control 3.49 r 0.10 3.23 2 0.16 3.37 c 0.18 PG 3.46 2 0.08 3.52 ‘- 0.08 4.12 r O.ll* Testosterone (ng/ml) Control 9.1 c 2.2 7.3 c 1.3 6.6 -c 1.2 PG 7.8 2 1.4 6.5 -f 0.9 7.6 2 1.2 Values are given as means 2 SEM (n=lO to 16). Statistically significant differences between pituitary-grafted (PC) and control mice; *p
FFA level and fat bodv weieht in PG mice. Pituitary grafting markedly decreased the serum FFA level, which dropped to 60 % of the control level at 3 months, and the low level was maintained throughout
the experimental
period (Fig. 3). In parallel with the decrease in serum FFA level, the
1175
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 1996
weight of the epididymal
fat body was significantly
lower in PG mice than the controls from 3-12
months after pituitary grafting. Histological observation of the epididymal fat body showed that the fat drops of adipose cells in PG mice at G months after receiving the graft were smaller than those in the control mice (Fig. 4) indicating the lipolytic effect of hyperprolactinemia.
Discussion Among the anterior pituitary hormones, be enhanced,
the release of PRL from the ectopic pituitary graft should
because PRL is regulated mainly by inhibitory factors from the hypothalamus,
other anterior pituitary hormones
are preferentially controlled
by stimulatory
signals
while
(19). In fact,
%i 400 -
=2
E $ sl. 21 2
* **
k
;
”
j.%i_:
9 5 m(I)
01
’
3
6
9
I 12
Months after pituitary grafting
; .I
0
“I 0 1 2 3
6
9
1 12
Months after pituitary grafting
Fig. 3 Strum FFA levels and the weights of epididymal fat body expressed per 20 g BW in PG mice. Vertical bars indicate the SEM (n=lO tol6). There were significant differences in both fat body weight and serum FFA level between PG ( 0 ) and control ( 0 ) mice for 3-12 months after pituitary grafting. *p
Fig. 4 HE-stained section of the epididymal fat body from PG (A) and control (B) mice at 6 months after pituitary grafting. The fat drops of adipose cells are very small in PG mice. Bar indicates 100 pm.
1176
this study
Effect of PRL on Glucose aad Lipid
showed
that pituitary
grafting
induced
Vol. 58, No. 14,19%
consistent
hyperprolactinernia,which
was
maintained for one year without altering serum GH levels. Although hyperprolactinemia reportedly alters the secretion of gonadotropins from the pituitary gland in S&A(20), the serum testosterone level did not change in our experimental model. In this study, the effect of chronic hyperprolactinemia into a hypoglycemic after 9 months. hypoglycemia.
on glucose metabolism
could be divided
phase that lasted until around 3 months and a hyperglycemic
phase that started
During the first 3 months the serum insulin level did not decrease, despite the PRL stimulates
(11-13) and lowering proliferation was the serum insulin be partly due to turnover (9) may
insulin secretion by enhancing
the threshold of insulin
pancreatic islet B-cell proliferation
secretion against glycemic stimulus
(21). B-cell
induced by hyperprolactinemia in our experimental model (16, 22). Therefore, in level remaining constant despite the hypoglycemia in PG mice was considered to the enhanced insulin secretion by PRL. PRL-induced enhancement of glucose have contributed to the hypoglycemia. PRL effects on the tension and pressure of
the blood (23) might have stimulated the radiation of heat in PG mice. circulation may be another cause of the hypoglycemia
This PRL effect on the
in PG mice. Pituitary grafting resulted in
lipolysis of adipose tissue despite enhanced insulin secretion, suggesting
the induction of insulin
resistance by PRL at that site. During the latter half of the experimental period, the blood glucose level was elevated, although the serum insulin level was high. This hyperinsulinemia may be partly due to increased insulin resistance, since hyperprolactinemia decrcascs responses to insulin by altering insulin receptors and post-receptor events in adipose tissue and muscle (6, 24). Changes in the activity of hepatic enzymes regulating glucose metabolism
(10) may also contribute to the hyperglycemia
in PG mice. The fact
that the serum level of FFA decreased along with the decrease in the weight of adipose tissue in PG mice, suggested that PRL enhanced lipid utilization in the tissues. Elevated FFA contributes to hepatic insulin resistance by competing
with glucose for utilization by insulin-sensitive
tissues (5,
25, 26). Hence, hyperglycemia and hypolipidimia in PG mice can be caused by an increase in lipid utilization in tissues, instead of glucose as the energy source. In addition, the increase in food intake and the corresponding
increase in digestive function (14, 16) may be rclatcd to the hyperglycemia
in
PG mice.
We are grateful to Dr. A. F. Parlow, Pituitary Hormones and Antisera Ccntcr, Harbor-UCLA Medical Center, for the mouse PRL RIA kit and mouse GH and to Dr. S. Raiti, the National Hormone and Pituitary Program of the NIDDK, for the mouse GH RIA kit. Thanks are also due to Dr. K. Wakabayashi, Instilutc for Molecular and Cellular Biorcgulation, Gunma University, for the second antibody for the RIAThis research was supported by a Research Grant from JSPS Research Fellowships for Young Scientists and a Sasagawa Scientific Research Grant from the Japan Science Society to M. Matsuda, and a Grants-in-Aid for Scientific Research and Developmental Scientific Research from the Ministry of Education, Science and Culture, Japan to T. Mori and M. K. Park.
1177
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 1996
ences 1. G. N. WADE and J. E. SCHNEIDER, 2.
D. H. WILLIAMSON,
3.
F. J. FIELDER and F. TALAMANTES,
Ncurosci. Biobehav. Rev. &235-272
Reprod. Nutr. Develop. zk597-603 Endocrinology
(1992).
(1986).
12493-497
(1987).
4. R. G. VERNON and D. J. FLINT, Proc. Nutr. Sot. 42315-331 (1983). 5. D. E. BAUMAN and W. B. CURRIE, J. Dairy Sci. ti 1514-1529 (1980). 6. C. M. OLLER DC NASCIMENTO, V. ILIC and D. H. WILLIAMSON,
Biochem.
J. 258
273-278 (1989) 7.
R. LANDGRAF, M. M. C. LANDGRAF-LEURS, A. WEISSMANN, R. HORL, K. VON WERDER and P. C. SCRIBA, Diabetologia =99-104 (1977). 8. T. MORI, T. IGUCHI, S. OZAWA, Y. UESUGI, N. TAKASUGI and H. NAGASAWA, Zool. Sci. 8339-343 (1991). 9. I. RATHGEB, R. WINKLER,
R. STEELE and N. ALTSZULER,
Endocrinology
&$718-722
(1971) 10. T. M. K. KUMARI and P. GOVINDARAJULU, Endocrinol. Japon z 819-825 (1990). 11. I. C. GREEN and K. W. TAYLOR, J. Endocrinol. 54317-325 (1972). 12. J. H. NIELSEN, Endocrinology m 600-606 (1982). 13. T. C. BRELJE, D. W. SCHARP, P. E. LACY, L. OGREN, ROBERTSON, 14.
M. MATSUDA, Endocrinol.
Endocrinology
m
F. TALAMANTES
and M.
and S. KAWASHIMA,
Eur. J.
879-887 (1993).
T. MORI, M. K. PARK, N. YANAIHARA
l,X! 187-194 (1994).
15.
H. NAGASAWA, R. YANAI, H. TANIGUCHI, R. TOKUZEN Natl. Cancer Inst. =425-430 (1976). 16. M. MATSUDA, T. MORI, M. K. PARK and S. KAWASHIMA, 221-226 (1995).
and W. NAKAHARA, Eur. J. Endocrinol.
J. m
17.
L. P. CAULEY, F. E. SPEAR and R. KENDALL, Am. J. Clin. Pathol. 32 195-200 (1959).
18.
S. SHIMIZU, K. YASUI, Y. TAN1 and H. YAMADA, Biochem. Biophys. 2 108-113 (1979).
19.
M. E. MOLITCH, Endoh_inoloev (Eds), 220-270, McGraw-Hill
Res. Commun.
P. Felig, J. D. Baxter and L. A. Frohman
Inc. (1995)
20.
T. SINGTRIPOP,
21.
2 145-150 (1993). R. L. SORENSON, T. C. BRELJE, 0. D. HEGRE, S. MARSHALL, SHERIDAN, Endocrinology 1211447-1453 (1987).
T. MORI, K. SHIRAISHI,
M. K. PARK and S. KAWASHIMA,
22.
T. MORI, H. NAGASAWA, (1986).
23.
D. E. MILLS and R. P. WARD, Proc. Sot. Exp. Biol. Med. 1813-8
24.
G. SCHRENTHANER, 28 138-142 (1985).
P. ANAYA and .I. D.
H. NAMIKI and K. NIKI, J. Natl. Cancer Inst. z
R. PRAGER, R. BONADONNA,
C. PUNZENGRUBER G. BUZZIGOLI,
In vivo
1193-1198
(1986)
and A. ZUGER, C. BONI,
Diabetologia
25.
S. BEVILACQUA,
26.
MACCARI, M. A. GIORICO and E. FERRANNINI, Metab. Clin. Exp. s 502-506 (1987) M. GILBERT, M. C. PERE, A. BAUDELIN and F. C. BATI’AGLIA, Am. J. Physiol. m E938-945 (1991).
D. CIOCIARO,
F.
PII SO0243205(96)0007S-6
ELSEVIER
CHRONIC EFFECT OF HYPERPROLACTINEMIA
ON BLOOD
GLUCOSE AND LIPID LEVELS IN MICE Manabu Matsuda, Takao Mori, Shuji Sassa’, Shinobu Sakamoto*, Mm Kyun Park and Seiichiro Kawashima Department of Biological Sciences, Graduate School of Science, University of Tokyo, and *Department of Endocrinology, Tokyo Medical and Dental University,
Medical Research Institute, Bunkyo-ku,
Tokyo 113, Japan
(Received in final form January 31, 1996)
We studied the chronic effects of hyperprolactinemia, grafting, on
induced by ectopic pituitary
blood glucose and lipid levels in adult male mice. For one year after
pituitary grafting, we measured the blood levels of prolactin, growth hormone (GH), insulin, glucose and free fatty acid (FFA) at various intervals. The graft caused consistent hyperprolactinemia
without changes in the serum GH levels. Hypoglycemia
developed at 1 and 3 months after grafting but was not accompanied by any changes of the serum insulin levels. Thereafter, the blood glucose and strum insulin levels began to increase in the pituitary-grafted (PG) mice, and at 12 months after the operation, both levels became significantly higher in PG mice than controls. The serum FFA levels and the weight of epididymal fat bodies were significantly lower in PG mice than controls from 3-12 months after the grafting. Thus, hyperprolactinemia leads to persistent hypolipidemia
and biphasic changes in the blood glucose level.
Key Work: hyperprolactinemic mice, glucose metabolism, lipid metabolism, insulin
Lactation induces changes in the metabolism not only of mammary gland but also of other organs, and requires a coordinated adaptation of metabolism in the whole body, especially in small mammals such as mice (1-3). For example, lipogenesis increases in mammary glands, while lipolysis increases in the adipose tissue of lactating animals (4). In many mammals prolactin (PRL) plays a principal role in the control of partition and utilization of metabolic fuels during lactation (5). Some Correspondence:
Matsuda, M., Laboratory of Endocrinology,
Department of Biological Sciences,
Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. Phone:81-3-3812-2111ex.4436, Fax:81-3-3816-1965, e-mail: [email protected]
1172
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 19%
of these PRL effects are direct, and the others are thought to be indirect, according to changes in the circulating levels of insulin, tissue insulin receptors and post-receptor cvcnts (1, 6). Chronic
hyperprolactinemia
lcads to metabolic
’ diabetogenic hormone’ (7). Hyperprolactinemia due to the reduction
of glycolysis
disorders,
and PRL
is followed by hyperglycemia
in the liver (10). On the other hand,
is sometimes
called
(8, 9) which is partly PRL stimulates
the
proliferation of pancreatic islet B-cells and insulin secretion (11-13) and hyperprolactinemia induces hypoglycemia in mice (14). Thus, the effects of hypcrprolactinemia on fuel metabolism are considered to differ among experimental animals. To study the effects of chronic hyperprolactinemia on fuel metabolism in mice, we investigated blood glucose and free fatty acid (FFA) levels after cctopic pituitary grafting, with special reference to insulin levels. Methods Animals.
Male mice of the SHN strain (15) were housed in plastic cages with wood shavings
under controlled temperature (25 2 0.5 “C) and light (12 h of light from 6:00 to 18:OO). They were given a commercial diet (CE-7, CLEA Japan, Inc., Tokyo) and tap water ad libitum. All procedures used on the mice were described in detail in a protocol that was approved by the Animal Care and USC Committee of the Graduate School of Sdcncc, University of Tokyo. Mice were divided sham-operated
into a hyperprolactincmic
group bearing pituitary grafts (PG mice) and a
group (control mice). In PG mice, an anterior pituitary gland obtained from female
litter-mates was grafted under the left kidney capsule at 2 months of age
Both groups of mice were
weighed and killed between 13:00 and 14:00 at 0.5, 1, 3, 6, 9, 12 months after the grafting. Control mice were also killed at comparable ages. Blood samples were collected from the trunk for measuring circulating levels of glucose, FFA, growth hormone (GH), PRL, testosterone and insulin. The liver and epididymal fat body were weighed. The fat body was fixed in Bouin’s solution and prepared as 4-pm paraffin sections for hematoxylin-eosin (HE) staining. In addition, food intake was measured by the difference between the initial and final weights of food baskets for 5 days before sacrifice. Glucose. FFA and hormone determination. levels were determined
Blood glucose and serum FFA, PRL, GH and insulin
as described (16). Briefly, the blood glucose level was determined by the
glucose oxidase method (17) (Scrapaper; Eiken, Tokyo). Serum FFA lcvcl was determined using acyl-CoA synthetase and acyl-CoA oxidase reaction (18) (NEFA C-test; Wako, Tokyo). Serum PRL levels were determined by means of a homologous RIA using kit donated by Dr. A. F. Parlow (Harbor-UCLA Medical Center). Serum GH levels were measured by means of a heterologous RIA using kit donated by Dr. S. Raiti (NIDDK) and a mouse GH standard from Dr. A F. Parlow. Serum insulin levels were determined by a heterologous enzyme immunoassay (Glazyme Insulin E&Test; Wako, Tokyo). Testosterone was measured using an RIA kit (Daiichi Radioisotope Labs., Ltd., Tokyo). . . w Student’s
Differences between the means of two groups were statistically evaluated by t-test or the Cochran-Cox test, when a significant difference in variance between two
Vol. 58, No. 14, 1996
1173
Effect of PRL on Glucose and Lipid
groups was found by Bartlett’s test for the uniformity
of variance. P values of less than 5 % were
considered significant.
Results Changes in the strum PRL and GH lcvcls in PG mice are shown
PRL
in Fig. 1. In PG mice, serum PRL levels wcrc clcvated to more than ten fold those of the controls by 1 month, and the elevated lcvcl remained constant thereafter. In PG mice, there was no significant difference in the serum PRL levels was observed bctwccn 0.5 and 12 months. On the other hand, serum GH levels were little affected by the graft throughout the cxpcrimcntal period,
the level in
PG mice being esscnthally similar to that in control mice (Fig. 1).
-0
01
3
6
Months after pituitary
9
12
grafting
“01
3
6
Months after pituitary
9
12
grafting
Fig. 1 Serum prolactin (PRL) and growth hormone (GH) levels in PG mice. Vertical bars indicate the SEM (n=lO to16). There were significant differences in the strum PRL level between PG ( l ) and control ( 0 ) mice for 0.512 months after pituitary grafting. **p
. . As shown in Fig. 2, hypoglycemia was induced at 1 and 3 Glucose levels in PG ti months after the pituitary grafting. The blood glucose levels in PG mice returned to the level of control mice at 6 months,
then significantly
increased at 12 months. Serum insulin levels also were
affected by pituitary grafting. The levels decreased little at 1 and 3 months after the pituitary grafting, despite hypoglycemia. Thereafter, the insulin levels gradually increased and became significantly higher in PG mice when compared with the controls at 12 months. The body weight (BW) and that of the liver, expressed per 20 g BW, were not altered at 3 and G months after pituitary grafting, but they increased significantly between 9 and 12 months in PG mice (Table 1, data at 6 and 12 months not shown). Food intake also increased at the same time in PG mice. Serum testosterone period.
levels were not significantly
altered by the graft during the experimental
1174
Effect of PRL on Glucose and Lipid
01
3
6
9
Vol. 58, No. 14, 1996
12
Months after pituitary grafting Fig. 2 Blood glucose and serum insulin levels in PG mice. Vertical bars indicate the SEM (n=lO tol6). There were significant differences in blood glucose levels at 1, 3, and 12 months and in the serum insulin level at 12 months between PG ( l ) and control ( 0 ) mice. *p
TABLE 1 Effect of Pituitary Grafting on the Body and Liver Weight, Food Intake and Strum Testosterone
Level. 1
Months after pituitary grafting 3
9 Body weight (g) Control 26.7 c 0.3 28.1 r 0.8 28.2 r 1.0 PG 27.4 * 0.3 29.5 -e 0.6 33.R t 1.0* Weight of Iiver (g/2Og SW) Control 1.01 -f 0.03 0.99 f 0.05 1.00 * 0.03 PG 1.00 + 0.03 1.04 f 0.03 1.12 + 0.06’ Food intake (g/day/20g SW) Control 3.49 r 0.10 3.23 2 0.16 3.37 c 0.18 PG 3.46 2 0.08 3.52 ‘- 0.08 4.12 r O.ll* Testosterone (ng/ml) Control 9.1 c 2.2 7.3 c 1.3 6.6 -c 1.2 PG 7.8 2 1.4 6.5 -f 0.9 7.6 2 1.2 Values are given as means 2 SEM (n=lO to 16). Statistically significant differences between pituitary-grafted (PC) and control mice; *p
FFA level and fat bodv weieht in PG mice. Pituitary grafting markedly decreased the serum FFA level, which dropped to 60 % of the control level at 3 months, and the low level was maintained throughout
the experimental
period (Fig. 3). In parallel with the decrease in serum FFA level, the
1175
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 1996
weight of the epididymal
fat body was significantly
lower in PG mice than the controls from 3-12
months after pituitary grafting. Histological observation of the epididymal fat body showed that the fat drops of adipose cells in PG mice at G months after receiving the graft were smaller than those in the control mice (Fig. 4) indicating the lipolytic effect of hyperprolactinemia.
Discussion Among the anterior pituitary hormones, be enhanced,
the release of PRL from the ectopic pituitary graft should
because PRL is regulated mainly by inhibitory factors from the hypothalamus,
other anterior pituitary hormones
are preferentially controlled
by stimulatory
signals
while
(19). In fact,
%i 400 -
=2
E $ sl. 21 2
* **
k
;
”
j.%i_:
9 5 m(I)
01
’
3
6
9
I 12
Months after pituitary grafting
; .I
0
“I 0 1 2 3
6
9
1 12
Months after pituitary grafting
Fig. 3 Strum FFA levels and the weights of epididymal fat body expressed per 20 g BW in PG mice. Vertical bars indicate the SEM (n=lO tol6). There were significant differences in both fat body weight and serum FFA level between PG ( 0 ) and control ( 0 ) mice for 3-12 months after pituitary grafting. *p
Fig. 4 HE-stained section of the epididymal fat body from PG (A) and control (B) mice at 6 months after pituitary grafting. The fat drops of adipose cells are very small in PG mice. Bar indicates 100 pm.
1176
this study
Effect of PRL on Glucose aad Lipid
showed
that pituitary
grafting
induced
Vol. 58, No. 14,19%
consistent
hyperprolactinernia,which
was
maintained for one year without altering serum GH levels. Although hyperprolactinemia reportedly alters the secretion of gonadotropins from the pituitary gland in S&A(20), the serum testosterone level did not change in our experimental model. In this study, the effect of chronic hyperprolactinemia into a hypoglycemic after 9 months. hypoglycemia.
on glucose metabolism
could be divided
phase that lasted until around 3 months and a hyperglycemic
phase that started
During the first 3 months the serum insulin level did not decrease, despite the PRL stimulates
(11-13) and lowering proliferation was the serum insulin be partly due to turnover (9) may
insulin secretion by enhancing
the threshold of insulin
pancreatic islet B-cell proliferation
secretion against glycemic stimulus
(21). B-cell
induced by hyperprolactinemia in our experimental model (16, 22). Therefore, in level remaining constant despite the hypoglycemia in PG mice was considered to the enhanced insulin secretion by PRL. PRL-induced enhancement of glucose have contributed to the hypoglycemia. PRL effects on the tension and pressure of
the blood (23) might have stimulated the radiation of heat in PG mice. circulation may be another cause of the hypoglycemia
This PRL effect on the
in PG mice. Pituitary grafting resulted in
lipolysis of adipose tissue despite enhanced insulin secretion, suggesting
the induction of insulin
resistance by PRL at that site. During the latter half of the experimental period, the blood glucose level was elevated, although the serum insulin level was high. This hyperinsulinemia may be partly due to increased insulin resistance, since hyperprolactinemia decrcascs responses to insulin by altering insulin receptors and post-receptor events in adipose tissue and muscle (6, 24). Changes in the activity of hepatic enzymes regulating glucose metabolism
(10) may also contribute to the hyperglycemia
in PG mice. The fact
that the serum level of FFA decreased along with the decrease in the weight of adipose tissue in PG mice, suggested that PRL enhanced lipid utilization in the tissues. Elevated FFA contributes to hepatic insulin resistance by competing
with glucose for utilization by insulin-sensitive
tissues (5,
25, 26). Hence, hyperglycemia and hypolipidimia in PG mice can be caused by an increase in lipid utilization in tissues, instead of glucose as the energy source. In addition, the increase in food intake and the corresponding
increase in digestive function (14, 16) may be rclatcd to the hyperglycemia
in
PG mice.
We are grateful to Dr. A. F. Parlow, Pituitary Hormones and Antisera Ccntcr, Harbor-UCLA Medical Center, for the mouse PRL RIA kit and mouse GH and to Dr. S. Raiti, the National Hormone and Pituitary Program of the NIDDK, for the mouse GH RIA kit. Thanks are also due to Dr. K. Wakabayashi, Instilutc for Molecular and Cellular Biorcgulation, Gunma University, for the second antibody for the RIAThis research was supported by a Research Grant from JSPS Research Fellowships for Young Scientists and a Sasagawa Scientific Research Grant from the Japan Science Society to M. Matsuda, and a Grants-in-Aid for Scientific Research and Developmental Scientific Research from the Ministry of Education, Science and Culture, Japan to T. Mori and M. K. Park.
1177
Effect of PRL on Glucose and Lipid
Vol. 58, No. 14, 1996
ences 1. G. N. WADE and J. E. SCHNEIDER, 2.
D. H. WILLIAMSON,
3.
F. J. FIELDER and F. TALAMANTES,
Ncurosci. Biobehav. Rev. &235-272
Reprod. Nutr. Develop. zk597-603 Endocrinology
(1992).
(1986).
12493-497
(1987).
4. R. G. VERNON and D. J. FLINT, Proc. Nutr. Sot. 42315-331 (1983). 5. D. E. BAUMAN and W. B. CURRIE, J. Dairy Sci. ti 1514-1529 (1980). 6. C. M. OLLER DC NASCIMENTO, V. ILIC and D. H. WILLIAMSON,
Biochem.
J. 258
273-278 (1989) 7.
R. LANDGRAF, M. M. C. LANDGRAF-LEURS, A. WEISSMANN, R. HORL, K. VON WERDER and P. C. SCRIBA, Diabetologia =99-104 (1977). 8. T. MORI, T. IGUCHI, S. OZAWA, Y. UESUGI, N. TAKASUGI and H. NAGASAWA, Zool. Sci. 8339-343 (1991). 9. I. RATHGEB, R. WINKLER,
R. STEELE and N. ALTSZULER,
Endocrinology
&$718-722
(1971) 10. T. M. K. KUMARI and P. GOVINDARAJULU, Endocrinol. Japon z 819-825 (1990). 11. I. C. GREEN and K. W. TAYLOR, J. Endocrinol. 54317-325 (1972). 12. J. H. NIELSEN, Endocrinology m 600-606 (1982). 13. T. C. BRELJE, D. W. SCHARP, P. E. LACY, L. OGREN, ROBERTSON, 14.
M. MATSUDA, Endocrinol.
Endocrinology
m
F. TALAMANTES
and M.
and S. KAWASHIMA,
Eur. J.
879-887 (1993).
T. MORI, M. K. PARK, N. YANAIHARA
l,X! 187-194 (1994).
15.
H. NAGASAWA, R. YANAI, H. TANIGUCHI, R. TOKUZEN Natl. Cancer Inst. =425-430 (1976). 16. M. MATSUDA, T. MORI, M. K. PARK and S. KAWASHIMA, 221-226 (1995).
and W. NAKAHARA, Eur. J. Endocrinol.
J. m
17.
L. P. CAULEY, F. E. SPEAR and R. KENDALL, Am. J. Clin. Pathol. 32 195-200 (1959).
18.
S. SHIMIZU, K. YASUI, Y. TAN1 and H. YAMADA, Biochem. Biophys. 2 108-113 (1979).
19.
M. E. MOLITCH, Endoh_inoloev (Eds), 220-270, McGraw-Hill
Res. Commun.
P. Felig, J. D. Baxter and L. A. Frohman
Inc. (1995)
20.
T. SINGTRIPOP,
21.
2 145-150 (1993). R. L. SORENSON, T. C. BRELJE, 0. D. HEGRE, S. MARSHALL, SHERIDAN, Endocrinology 1211447-1453 (1987).
T. MORI, K. SHIRAISHI,
M. K. PARK and S. KAWASHIMA,
22.
T. MORI, H. NAGASAWA, (1986).
23.
D. E. MILLS and R. P. WARD, Proc. Sot. Exp. Biol. Med. 1813-8
24.
G. SCHRENTHANER, 28 138-142 (1985).
P. ANAYA and .I. D.
H. NAMIKI and K. NIKI, J. Natl. Cancer Inst. z
R. PRAGER, R. BONADONNA,
C. PUNZENGRUBER G. BUZZIGOLI,
In vivo
1193-1198
(1986)
and A. ZUGER, C. BONI,
Diabetologia
25.
S. BEVILACQUA,
26.
MACCARI, M. A. GIORICO and E. FERRANNINI, Metab. Clin. Exp. s 502-506 (1987) M. GILBERT, M. C. PERE, A. BAUDELIN and F. C. BATI’AGLIA, Am. J. Physiol. m E938-945 (1991).
D. CIOCIARO,
F.