The effect of estradiol on isolated rat uterine motility and on prostaglandin generation

The motility of isolated uterine horns as well as the generation of PGE and PGF like material by the uterus from estrus and spayed rats, treated or untreated with 17-beta estradicl, were studied. Following 40 minutes of mounting the spontaneous motility of uteri from estrus rats had a lower magnitude than that from spayed ones. The amount of PGF-like material was similar in both groups whereas the first one liberated less PGE-like substance. In spayed animals treated with 1 μg of 17-beta estradiol the decay of spontaneous contractile force was higher than that observed in untreated rats, and similar to that displayed by uteri from estrus. Less PGE-like material was liberated in comparison with spayed animals and a tendency to produce higher quantity of PGF-like compounds was observed, although the level was not significantly different. With 50 μg of 17-beta estradiol the spontaneous reduction of contractile activity was higher than in spayed animals and than in those treated with 1 μg. The amount of PGF-like material liberated was higher than in spayed rats and less PGE-like substance was generated comparing with spayed and 1 μg-treated animals. These findings show that estradiol decreases the release of PGE-like compound. It would also appear that this may have some relationship with the levels of spontaneous contractile activity of the isolated rat uterus.     

Effect of prolactin and estradiol on rat striatal dopamine receptors

Chronic estrogen treatment has been found to increase the level of rat striatal dopamine receptors. Since it is well known that estrogen treatment increases circulating prolactin levels, we have investigated the possibility that the stimulatory effect of estrogens on dopamine receptors is exerted via prolactin. Ovariectomized female or intact male rats were implanted with three adenohypophyses under the kidney capsule or treated with 17 β-estradiol (10 μg, twice daily) for 2 weeks. In animals of both sexes, the pituitary-implanted and estradiol-treated rats showed higher levels of [³H]spiperone binding to striatal dopamine receptors. This effect of estradiol or pituitary implants on dopamine receptors was further investigated in ovariectomized rats. The pituitary-implanted and estradiol-treated rats had elevated plasma prolactin levels and an increased density of striatal dopamine receptors without alteration of their affinity. The role of the pituitary in the effect of estradiol was next investigated using hypophysectomized female rats treated with 17 β-estradiol (10 μg, twice daily), o-prolactin (500 μg, twice daily) or bearing three anterior pituitary implants. The implants as well as the treatment with estradiol or prolactin increased the level of striatal dopamine receptors in hypophysectomized rats while, as expected, the estradiol-treated animals did not have elevated plasma prolactin levels. The present data indicate that high prolactin levels lead, as observed with chronic estradiol treatment, to an increased density of striatal dopamine receptors. However, the effect of estradiol may not be explained exclusively by increased prolactin levels since a similar stimulatory effect is observed in hypophysectomized animals.     

Influences of estradiol and of catechol and non-catechol estrogens on the output of prostaglandins in uteri from spayed rats

The effects of 17-beta estradiol and of some catechol and non-catechol-estrogens on the synthesis and output of prostaglandins (PGs) E and F by uteri from ovariectomized rats, were explored. Uteri from castrated animals released twice as much PGE than PGF. When uterine tissue was obtained from spayed rats injected prior to sacrifice with a low dose of 17-beta estradiol (0.5 + 1.0 microgram, on two consecutive days), the output of PGE diminished significantly. With a higher dose of the hormone (0.5 + 50.0 micrograms) the depressive influence on the synthesis and release of PGE was even more marked, whereas the output of PGF rose significantly. Low or high doses of estrone or of estriol failed to affect the release of either one of the PGs determined. On the other hand, 2-0H-estradiol at a low dose had no action but at a higher one inhibited the release of PGE without influencing PGF. Neither low nor high doses of 2-0H estriol or of 2-0H estrone affected the synthesis and release of uterine PGs. It was also observed that all the compounds tested evoked a significant uterotrophic action. It appears plausible that some catechol metabolites of 17-beta estradiol, but not other catechol-estrogens, could be involved in the mechanism of action of 17-beta estradiol modulating the production of PGs by the rat uterus.     

Progesterone receptor gene and protein expression in the anterior preoptic area and hypothalamus of defeminized rats

Progesterone receptor (PR) plays an important role during sexual differentiation of the rat brain. The objective of the present study was to determine PR protein and gene expression pattern in preoptic-anterior hypothalamic area (POA-AHA) and hypothalamus (HYP), after estradiol or testosterone treatment during the postnatal critical period of sexual differentiation of the rat brain (defeminized animals). Three-day-old female rats were subcutaneously (s.c.) injected with a single dose of 17beta-estradiol (200 microg), or testosterone enanthate (200 microg), or vehicle (corn oil). POA-AHA and HYP were dissected 3 h, 24 h, and 14 days, as well as on the day of vaginal opening (VO) after treatments. Other animals, previously treated as above, were acutely injected with 17beta-estradiol (5 microg) on the day of VO; POA-AHA and HYP were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR and tissue slices were prepared for protein detection by immunohistochemistry. We observed that PR mRNA expression was increased in POA-AHA and HYP of the animals treated with estradiol or testosterone 3 hours after treatments, compared with the vehicle-treated control group. We also found a significant increase in PR mRNA and protein expression in POA-AHA and HYP on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute administration of estradiol on the day of VO (VO + E(2)) did not increase PR mRNA or protein expression in POA-AHA and HYP of either estradiol or testosterone defeminized animals, as opposed to the marked induction observed in the intact animals of the control group. The overall results suggest that estradiol and testosterone treatment during the postnatal critical period of sexual differentiation of the brain modifies the regulation of the PR mRNA and protein expression during early onset of maturity.     

Influence of sex hormones on prostaglandin dehydrogenase activity in the rat uterus

The present experiments report the effects of estradiol or of progesterone on the activity of 15-prostaglandin-dehydrogenase (PGDH) in the uterus of spayed rats. When the substrate was PGF2 alpha the treatment with progesterone (4 mg X day-1, two days) or with estradiol-17-beta (0.5 ug + 1 ug) did not show any effect on the activity of the enzyme. On the contrary, uteri from ovariectomized rats injected with a higher dose of estradiol-17-beta (0.5 ug + 50 ug) exhibited a significant increment. When the substrate was PGE2, progesterone failed again to modify the enzyme activity, whereas estradiol, both at a low and at a high doses, enhanced significantly the uterine PGDH activity. The possibility of two different PGDHs for each PG and the role of estradiol in enhancing PGE2 catabolism into 15-keto-PGE2 as a mechanism subserving the effect of estrogens on the output of this PG in the rat uterus, are discussed.     

Regulation of hepatic apolipoprotein synthesis in the 17 alpha-ethinyl estradiol-treated rat

Regulatory mechanisms of hepatic apolipoprotein synthesis were studied in groups of male Sprague-Dawley rats made severely hypolipidemic by treatment with pharmacological doses of 17 alpha-ethinyl estradiol. Treatment resulted in a marked reduction of plasma cholesterol and apolipoproteins B, A-I, and A-IV. Hepatic apoA-I mRNA and apoA-I synthesis were increased in the ethinyl estradiol-treated animals. Hepatic apoA-IV protein synthesis rates were unaltered; however, a reduction of the apoA-IV mRNA level was observed. Diet-control studies suggested the effects of 17 alpha-ethinyl estradiol on apoA-I, unlike those on apoA-IV, appeared to be related to the steroid and not to reduced caloric intake. Livers of control and ethinyl estradiol-treated rats synthesized both apoBH and apoBL. Total hepatic apoB (apoBL plus apoBH) synthesis and apoB mRNA levels in the ethinyl estradiol-treated rats were similar to ad libitum fed or diet-controls. In ad libitum fed and diet-control rats, 21% and 32%, respectively, of newly synthesized hepatic apoB was apoBH. In contrast, 47% of the newly synthesized apoB in the ethinyl estradiol-treated animal was apoBH. Nucleotide sequence analysis of hepatic apoB mRNA confirmed a marked decrease in the proportion of the apoBL mRNA in ethinyl estradiol-treated animals. After cessation of 17 alpha-ethinyl estradiol treatment, the hepatic apolipoprotein A-I synthesis rate, apolipoprotein A-I and A-IV mRNA levels, and the apoBH and apoBL synthesis rates, as well as plasma apolipoprotein and cholesterol levels, returned to normal. A major finding of the present study is that pharmacological doses of ethinyl estradiol do not affect total hepatic apoB synthesis, but increase the relative amount of apoBH synthesized.     

Quantitative variations in the number and size of peritoneal mastocytes in the female rat during the normal sexual cycle, following ovariectomy and administration of estrogens

Female rat peritoneal mast cells were found more numerous and of more reduced sizes in metestrus and diestrus than in proestrus and especially estrus where a partial degranulation took place. Ovariectomy caused an important decrease in the number and size of mast cells. A regular treatment of spayed animals by 17 beta estradiol partly inhibited these effects.     

Diurnal variations in estradiol binding site concentrations in the hypothalamus, pituitary and uterus of prepuberal rats

Available cytosolic estradiol binding sites (EBS) were estimated at 6 h intervals over a 24 h period in individual extracts of uteri, pituitaries and hypothalami from intact, ovariectomized or hypophysectomized 28-day old rats, maintained from birth in a 12 h light-12 h dark photoperiod. Plasma estrogen levels were also recorded, in intact rats, they displayed a 20% rise during daytime. In the uterus and pituitary of ovariectomized rats EBS concentrations exceeded by one third those of intact controls. In intact animals, significant diurnal variations in EBS were observed in both these tissues, with increased daytime levels. These variations appeared to depend on the amount of estrogen in the plasma, as they were not observed in spayed rats. No diurnal variations in EBS were apparent in the hypothalamus of intact animals, but they did occur in ovariectomized rats, and even more significantly in hypophysectomized rats, although the latter had lower EBS concentrations than spayed animals. These variations were presumed to result from the interference of pituitary-controlled hormones other than estrogens in the regulation of EBS levels.     

Role of ovarian secretion in the development of dysfunction in the regulation of luteinizing hormone secretion in female rats exposed to constant illumination.

Female rats in constant illumination (LL) fail to show the facilitation of LH release following steroid administration that is characteristic of animals in normal lighting. To determine whether this effect is mediated through changes in ovarian function, rats were spayed either at the time of placement into different lighting schedules (LL or a 14:10 light-dark (LD) schedule) or 10 weeks later, and their plasma LH responses to steroids were compared after an additional 3-week exposure to the experimental lighting conditions. To test the LH response, estradiol benzoate (EB) was injected at 12.00 h and followed 72 h later by injection of progesterone (P) or a second injection of EB. Neither steroid regime revealed differences in LH release between animals ovariectomized at the time of placement into LL and those spayed 10 weeks later. The duration of castration in animals in LD affected the LH response to a priming dose of EB, but not to a second dose of EB or to P. It is concluded that altered ovarian activity is not the factor which mediates the loss of a facilitatory response of LH release following administration of gonadal steroids to rats under constant illumination.     

The role of the pituitary in modifications of the uterine secretion of spayed, oestradiol-primed rats

Tests performed on spayed, adult female estradiol-primed Ivanovas rats, with ligated uteri and normal pituitary function have shown that treatment with sexual steroids, including progesterone and testosterone, modifies uterine secretion. One half of the animals were hypophysectomized. In estradiol primed hypophysectomized controls, growth was retarded about 28%, the weight of the empty uterus reduced, and the quantity of uterine secretion diminished in comparison with the values for the nonhypophysectomized controls. In test rats treated with estradiol, gain in body weight was virtually arrested in the nonhypophysectomized rats and a reduction in weight was observed in both groups treated with the highest dose of estradiol tested (300 mcg/kg daily). In rats treated with progesterone, no significant differences were found between the two groups. In treated groups, a dose-related reduction in the weight of the empty uterus was found. Treatment caused a marked reduction in the quantity of the uterine secretion, the effect appearing greater in nonhypophysectomized rats. Increasing doses of progesterone produced a rapid rise in the viscosity of the uterine fluid, as well as a decrease in the pH of the uterine lumen. In both hypophysectomized and nonhypophysectomized rats, testosterone induced a dose-related increase in body weight, statistically significant only in animals with intact pituitaries treated with 100 mg/kg daily. The weight of the empty uterus also increased. The quantity of uterine fluid was reduced by testosterone only when it was given in massive doses to nonhypophysectomized rats. Doses of 100-300 mg/kg daily were needed to produce the same response as a dose of about 10 mg/kg daily of progesterone. In response to large doses, viscosity of secretion rose slightly and the pH of uterine lumen and secretion decreased. It may be concluded that the progestative modifications induced by progesterone in the uterus of spayed, estradiol-primed rats, including particularly changes in uterine secretion, are the effects of a peripheral mechanism not involving the pituitary. Testosterone appears to be an exception as far as the quantity and viscosity of uterine secretion are concerned, since modifications in these parameters are only observed in the presence of a functional pituitary body.     

Ovarian hormones inhibit the release of prostacyclin-like material from isolated rat uterus

The influence of sex steroids on the production of prostacyclin (PGI₂) like material by the isolated rat uterus incubated in a buffer medium was explored by monitoring its ability to inhibit ADP-induced platelet aggregation. Chopped uterine strips from rats in natural estrus can generate an unstable substance that inhibits platelet aggregation and suggest to be prostacyclin. This capacity was significantly enhanced in preparations from spayed animals. The injection of 17-beta estradiol; progesterone or both diminished the production of the prostacyclin-like material by the uterus from ovariectomized rats. The already existing notion that ovarian steroids are able to regulate the synthesis of stable prostaglandins is discussed together with the present results suggesting in addition a depressive effect of sex hormones on the uterine PGI₂ synthetase system.     

Failure of neurotransmitter blockers to alter PGE2-induced LH release.

The purpose of this study is to ascertain whether or not prostaglandin (PG) E2 induces LH release by modifying or modulating the release or action of neural transmitters. PGE2 injected iv into spayed rats primed two days earlier with 10 microgram estradiol benzoate increased the plasma levels of LH 10 min later as measured by radioimmunoassay. The peak of plasma LH was not changed by prior treatment with beta- or alpha-adrenergic receptor blockers, propranolol or phenoxybenzamine. The peak level of plasma LH did not alter in rats treated with DL-alpha-methyl-p-tyrosine methyl ester HCl (alpha-MPT) or sodium diethyldithiocarbamate (DDC). Similarly, the peak of plasma LH was not changed by prior treatment with imipramine. Administration of PGE2 produced an increase in anterior pituitary and plasma, but not hypothalamic cyclic AMP concomitantly with the elevation in plasma LH. Although it is possible that the effect of PGE2 could be mediated by another transmitter system, as yet unknown, or that the effect of PGE2 on LH release could be mediated via the adenylate cyclase-cyclic AMP system, the results indicate that PGE2 does not act trans-synaptically, but probably acts directly on LH-RH neurons.     

Failure of neurotransmitter blockers to alter PGE2-induced LH release.

The purpose of this study is to ascertain whether or not prostaglandin (PG) E2 induces LH release by modifying or mudulating the release or action of neural transmitters. PGE2 injected inv into spayed rats primed two days earlier with 10 mug estradiol benzoate increased the plasma levels of LH 10 min later as measured by radio-immunoassay. The peak of plasma LH was not changed by prior treatment with beta- or alpha-adrenergic receptor blockers, propranolol or phenoxybenzamine. The peak level of plasma LH did not alter in rats treated with DL-alpha-methyl-ptyrosine methyl ester HC1 (alpha-MPT) or sodium diethyldithiocarbamate (DDC). Similarly, the peak of plasma LH was not changed by prior treatment with imipramine. Adminisration of PGE2 produced an increase in anterior pituitary and plasma, but not hypothalamic cyclic AMP concomitantly with the elevation in plasma LH. Although it is possible that the effect of PGE2 could be mediated by another transmitter system, as yet unknown, or that the effect of PGE2 on LH release could be mediated via the adenylate cyclase-cyclic AMP system, the results indicate that PGE2 does not act trans-synaptically, but probably acts directly on LH-RH neurons.     

Effect of progesterone on the spontaneous motility and prostaglandin synthesis in uterine horns isolated from ovariectomized rats

The motility of isolated uterine horns as well as the generation of PGE and PGF-like material by uterus from spayed rats, treated or untreated with progesterone or progesterone plus estradiol-17-beta, were studied. The changes of Functional Activity (FA) with time (constancy) of control uterine horns and that preparations treated wtih 2 mg of progesterone (P) were not significantly different. However, the PGF-like material released into the bathing solution was significantly higher when the animals were treated with P. PGE-like material in the medium was similar in both groups. With higher doses to P (4 mg/day/2 days) the constancy of FA was similar to that observed in untreated animals, and the PGF-like material released into the medium was significantly higher than in the control group FA and PGs releases into the bathing medium by uterine horns from supra-renalectomized-ovariectomized animals (treated or not with P) were similar to those obtained in spayed rats with the intact suprarenal gland, but the absolute values of PGF-like material were always lower than in this group. Estradiol-17-beta injected prior or after P diminished the stimulation induced by P on the release of PGF-like material into the medium. The constancy of the contractile activity as well as the uterine release of PGE-like material was also diminished in rats treated with P plus estradiol-17-beta. The novel finding that progesterone stimulates the synthesis of PGF in uterine horns from ovariectomized rats without changing that of PGE is discussed.     

Influence of sex hormones on prostaglandin dehydrogenase activity in the rat uterus

The present experiments report the effects of estradiol or of progesterone on the activity of 15-prostaglandin-dehydrogenase (PGDH) in the uterus of spayed rats. When the substrate was PGF_2α the treatment with progesterone (4 mg.day⁻¹, two days) or with estradiol-17-beta (0.5 ug + 1 ug) did not show any effect on the activity of the enzyme. On the contrary, uteri from ovariectomized rats injected with a higher dose of estradiol- 17-beta (0.5 ug + 50 ug) exhibited a significant increment. When the substrate was PGE₂, progesterone failed again to modify the enzyme activity, whereas estradiol, both at a low and at a high doses, enhanced significantly the uterine PGDH activity. The possibility of two different PGDHs for each PG and the role of estradiol in enhancing PGE₂ catabolism into 15-keto- PGE₂ as a mechanism subserving the effect of estrogens on the output of this PG in the rat uterus, are discussed.     

Estrogen regulation of tissue-specific expression of complement C3

The administration of estradiol to immature rats results in the increased synthesis and secretion of a 180-kDa protein, composed of 115- and 65-kDa subunits, by the uterine luminal epithelial cells. A monoclonal antibody against the 180-kDa protein was utilized to isolate the corresponding cDNA (LE-1) from a rat uterine luminal epithelial cell cDNA lambda gt11 expression library. This LE-1 cDNA was sequenced and shown to be homologous to complement component C3. The sequence was approximately 81 and 90% homologous to human and mouse C3, respectively. The LE-1 cDNA sequence was homologous with the 3' portion of the C3 mRNA containing the alpha subunit (115 kDa). Uterine mRNA isolated from immature rats treated with 1 microgram of estradiol for 24 h demonstrated a 25-fold increase in the concentration of a 6.0-kilobase mRNA by Northern hybridization with either LE-1 or authentic human C3 cDNA probes. To further examine the possibility that the estradiol-regulated secretory protein was C3, an aliquot of radiolabeled media protein from control and estradiol-stimulated rat uteri was incubated with goat anti-rat C3 antibody. The immunoprecipitated radiolabeled protein from estradiol-treated animals was increased significantly (p less than 0.01) compared to media from control animals. Analysis of the immunoprecipitated proteins on nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single protein of 180 kDa from estradiol-stimulated uterine media, whereas no detectable proteins were immunoprecipitated from media obtained from control uteri. Also, when the immunoprecipitated protein was reduced (20 mM dithiothreitol) it dissociated into two subunits of 115 and 65 kDa. Immunohistochemical studies demonstrated the presence of C3 only in the epithelial cells of estrogen-stimulated rat uteri. In addition, the estradiol-stimulated mRNA was only detectable in uterine epithelial cell RNA. Analysis of liver RNA demonstrated a 6.0-kilobase mRNA, as in the uterus, when hybridized with LE-1. However, unlike the uterus, its concentration was not influenced by estrogen administration with up to three daily injections of 100 micrograms of diethylstilbestrol. Based on biophysical, DNA sequence, and antibody data we conclude that rat uterine epithelial cells produce C3 in response to estradiol whereas the expression in the liver was not modulated by estrogens.     

Age-dependent induction and repression of rat liver microsomal hydroxylase systems by estradiol

The activities of the hepatic microsomal 2α-, 2β-, 18- and 7α-hydroxylase systems active on 5α-[4-^14C] androstane-3α,17β-diol were studied in male and female rats which had been castrated and spayed at 14, 24, 35 and 45 days of age, treated for 5 days with 500 μg of estradiol benzoate per kg body weight and killed 6 days after gonadectomy. The hepatic microsomal 15β-hydroxylase enzyme system active on 5α-[1,2-³H] androstane-3α, 17β-diol 3,17-disulphate was also measured in these animals as well as in an additional group of animals that were gonadectomized at 56 days of age, treated with estradiol benzoate and killed at 62 days of age. The hydroxylase systems active on the free steroid substrate were all relatively unresponsive towards enstradiol in the developing rat, in contrast to the strong effects on hepatic hydroxylase activities previously noted following treatment of adult male rats with estradiol. On the other hand, the 15β-hydroxylase system active on disulphurylated 5α-androstane-3α, 17β-diol was inducible in both male and female rats of 41 and 51 days of age and in male rats of 61 days of age.     

Uptake of estradiol by the rat pineal organ. Effects of cervical sympathectomy, stage of the estrous cycle and estradiol treatment

Rat pineal organs of spayed rats took up and retained estradiol $\text{in vitro}$ up to 32-fold the concentration present in the incubation media. This phenomenon was maximum at 37°C and after 2-h incubations. Most (86–91%) of [³H] radioactivity recovered from the incubated pineals was identified as estradiol by thin-layer chromatography. Treatment with dextran-coated charcoal of nuclei-free pineal homogenates incubated with [³H] estradiol of different SA uncovered a high affinity, low capacity binding of estradiol to cytosol components. Uptake of estradiol by the nuclear fraction also proceeded in a saturable fashion. Similar findings were made in uterine homogenates of spayed rats.Estradiol uptake by the pineal organ and the uterus of cycling rats varied as a function of the stage of the estrous cycle, maxima being observed in diestrus and minima in proestrus. The administration of a priming dose of estradiol benzoate to spayed rats caused high affinity binding components of the pineal cytosol to increase by about 150%. Nuclear binding of estradiol was also increased by the estradiol priming dose. Pineal denervation, i.e., by superior cervical ganglionectomy, caused pineal estradiol uptake to decrease significantly by about 20%. These data suggest that the early steps of estradiol action on the pineal organ may resemble those of the uterus.     

Oxytocin enhances the basal release of uterine prostaglandin F2 alpha, but not that of PGE1, or of PGE2, and changes the metabolism of exogenous arachidonate, favouring the formation of prostaglandin F2 alpha and 5-HETE. Relationships with its uterotonic action and modulation by estradiol

We attempted to explore possible mechanism(s) subserving the influence of oxytocin on uterine motility by studying the action of the hormone on: 1) the contractile activity of isolated rat uteri in the presence or absence of indomethacin; 2) the synthesis and release of prostaglandins (PGs) into the solution incubating the uterine tissue as well as the metabolism of labelled arachidonic acid; 3) the uptake of 45Ca2+ by uterine strips. The experiments were bone with uterine preparations isolated from spayed rats treated or not with 17-beta-estradiol. The values of isometric developed tension (IDT) and of frequency of contractions (FC) induced by oxytocin in uterine strips isolated from spayed and spayed-estrogenized rats, were not modified by indomethacin at 10(-6) M. On the other hand, uterine strips from untreated spayed rats, release into the incubating medium approximately equal amounts of PGE1, PGE2 and PGF2 alpha. The in vitro presence of oxytocin (50 mU/ml) increased significantly (p 0.05) the output of PGF 2 alpha without changing the release of PGE1 or PGE2. Uteri from spayed rats injected prior to sacrifice with 17-beta-estradiol released significantly less PGE1 and PGE2 (p less than 0.005) than preparations from non-injected animals, whereas the output of PGF2 alpha in the suspending solution remained unchanged. Following estrogenization the addition of oxytocin to preparations obtained from spayed-estrogenized rats also increased the output of uterine PGF2 alpha (p less than 0.001) without changing that of PGs E1 or E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of sex hormones on the onset of diabetic syndrome in WBN/Kob rats]

The effects of sex hormone on diabetic conditions were investigated in WBN/Kob strain rats, i.e., castrated or spayed, hormone-treated, and non-treated rats. The effects of sex hormone on glycosuria, body-weight change, glucose tolerance and histopathology of the pancreas were compared among these animals. There were no abnormal changes in these parameters in the non-treated females and estrogen-treated males. The glycosuria began to be observed from the age of about 30 weeks in the non-treated group and from the age of 52 weeks in the castrated group. In the female animals, this symptom began to appear from the age of 55 weeks in the testosterone-treated group and from the age of 72 weeks in the spayed group. Before the onset of the diabetic symptoms, glucose tolerance was impaired in these animals. Body weights of the castrated and estrogen-treated males were lower than that of the non-treated males, especially in the estrogen-treated males. Those of the spayed and testosterone-treated females were much heavier than that of the non-treated females. Testosterone treatment accelerated body-weight gain in the spayed female animals. Histopathological examination of the pancreas revealed atrophy of the aciner tissue and atrophy and disappearance of the islet cells similar to those of the non-treated WBN/Kob male rats in the castrated males, spayed females and testosterone-treated females. However, these changes were not observed in the non-treated females or estrogen-treated males. These findings suggest that female hormone suppressed the onset of hyperglycemia along with glycosuria and male hormone accelerates the onset of hyperglycemia in the WBN/Kob rats.