In vitro and in vivo assessment of plutonium speciation and decorporation in blood and target retention tissues after a systemic contamination followed by an early treatment with DTPA

This study identifies the main sources of systemic plutonium decorporated in the rat after DTPA i.v. at the dose recommended for humans (30 mumol kg(-1)). For this purpose, standard biokinetic approaches are combined to plasma ultrafiltration for separation of plutonium complexes according to their molecular weight. In vitro studies show that at the recommended DTPA dose, less than 5% of the plasma plutonium of contaminated rats can be displaced from high-molecular-weight ligands. After i.v. administration of Pu-DTPA, early ultrafiltrability of plutonium in plasma decreases with total DTPA dose, which is associated with an increase in plutonium bone retention. This demonstrates the instability of Pu-DTPA complexes, injected in vivo, below the minimal Ca-DTPA dose of 30 mumol kg(-1). Plutonium biokinetics is compared in rats contaminated by plutonium-citrate i.v. and treated or not with DTPA after 1 h. No significant decrease in plasma plutonium is observed for the first hour after treatment, and the fraction of low-molecular-weight plutonium in plasma is nearly constant [5.4% compared with 90% in Pu-DTPA i.v. (30 mumol kg(-1)) and 0.7% in controls]. Thus plutonium decorporation by DTPA is a slow process that mainly involves retention compartments other than the blood. Plutonium-ligand complexes formed during plutonium deposition in the retention organs appear to be the main source of decorporated plutonium.     

Modulation of glucose transporter (GLUT4) by vanadate and Trigonella in alloxan-diabetic rats

Oral administration of vanadate is an effective treatment for diabetes in animal models. However, vanadate exerts these effects at high doses and several toxic effects are produced. Low doses of vanadate are relatively safe but are unable to elicit any antidiabetic effect. The present study explored the prospect of using low doses of vanadate in combination with Trigonella seed powder (TSP) to evaluate their antidiabetic effect in alloxan-diabetic rats. Alloxan-diabetic rats were treated with insulin, vanadate, TSP and vanadate and TSP in combination for 3 weeks. The effect of these antidiabetic compounds was examined on general physiological parameters and distribution of glucose transporter (GLUT4) in skeletal muscle by immunoblotting and immunohistochemistry. Treatment of alloxan-diabetic rats with insulin, vanadate, TSP and vanadate in combination with TSP revived normoglycemia and restored the disturbances in the distribution of GLUT4 in skeletal muscle. TSP treatment was only partially effective in the restoration of diabetic alterations. The treatment of diabetic rats with combined doses of vanadate and TSP was most effective in the normalization of plasma glucose levels and correction of altered GLUT4 distribution.     

Biological effects of the enhanced excretion of zinc after calcium diethylenetriaminepentaacetate chelation therapy.

An enhanced, uncompensated excretion of zinc may be responsible for unwanted side-effects that could develop after prolonged chelation therapy with calcium diethylenetriaminepentaacetate (Ca-DTPA). As a preliminary means of defining "potential toxicity" within this hypothesis, the "normal" concentration range of Zn++ excreted in the urine of three adult female baboons was measured on a daily basis; changes in urinary Zn++ excretion were then quantitated as a function of the injection time and dose of the chelating agent Na3(Ca-DTPA) originally administered to enhance the excretion of 241Am from the body. In addition, the inhibitory action of the chelator compound on the activity of a specific metalloenzyme system, erythrocytic aminolevulinic acid dehydratase (ALAD), which requires Zn++ as a co-factor, has been determined as a measure of a specific biological effect. It was found that whenever the concentration of Zn++ in urine was above 2 mug/ml (or greater than approximately four times the "normal" urinary excretion level), the activity of ALAD dropped below 250 nmol PBG/ml RBC/hr or approximately one-half the mean "normal" activity value for this primate species.     

Effect of rIFN-gamma and IL-2 treatments in mouse and nude rat infections with Toxoplasma gondii.

Mice and nude rats lethally infected with T. gondii and treated with recombinant rat interferon-gamma (rIFN-gamma) or recombinant human interleukin-2 (rIL-2) were protected against death, when compared with untreated infected controls. In mice rIFN-gamma and rIL-2 played an important role in "prophylactic treatment", but not in "curative therapy". The survival rate was 42% in mice treated with 3 doses of 20,000 U of rIFN-gamma at days -2, -1, 0 before challenge and up to 66% in mice treated with 3 doses of 10,000 U of rIFN-gamma at days -2, 0, +2 before and after infection. Whereas the survival rate was 33% in mice that received 3 doses of 500 U rIL-2 at days -2, -1, 0 before infection, or -2, 0, +2 before and after infection respectively, up to 50% of the mice treated with 3 doses of 1,000 U rIL-2 at days -2, -1, 0 survived. In nude rats rIFN-gamma had a slight effect in "prophylactic treatment", whereas rIL-2 was active only in "curative treatment". The survival rate was 25% both in nude rats treated with doses of 400,000 U of rIFN-gamma at days -3, 0 before challenge, or with doses of 5,000 U of rIL-2 at days +2, +6, +9 after infection. These results lead us to hypothesise that the mechanism by which the lymphokine treatment exerts a protective effect on Toxoplasma infected mice is different from that on nu/nu rats. We conclude that these cytokines may play a notable role in modulating the host's immune defence against T. gondii infection.     

A karyometric and stereologic study of the effects of gonadotrophin and testosterone on the interstitial gland of the testis of intact and endoxan treated rats

Adult male rats were treated daily for 18 days with endoxan in doses of 4 mg/kg of body weight or testosterone in doses 2.5 mg per rat. For the last 5 days of the experiment some of the rats received gonadotrophin injections in doses of 50 I.U. Karyometric and stereologic studies were undertaken on paraffin sections of the testes stained with haematoxylin and eosin. Endoxan treatment decrease the nuclear volume of the Leydig cells and lowers the volume fraction occupied by the interstitial gland in the testis. These changes were accompanied by a decrease in the intensity of reaction for acid phosphatase, non-specific esterases and 3-beta-hydroxy-steroid dehydrogenase. Testosterone injected alone or jointly with endoxan resulted in more pronounced changes than following treatment with endoxan alone. As expected, gonadotrophin injections into intact rats resulted in a marked increase in nuclear volume of the Leydig cells and in the volume fraction of the interstitial gland. This effect of gonadotrophin on the interstitial gland of the rat testis was partially inhibited by endoxan treatment. It follows from these experiments that endoxan impairs the functional activity of the interstitial gland of the rat testes by lowering the endogenous gonadotrophin levels, as well as by direct action on the Leydig cells.     

Chronic treatment with high doses of haloperidol fails to decrease the time course for the development of depolarization inactivation of midbrain dopamine neurons

Using extracellular single unit recording techniques, we investigated the effects produced by chronic treatment with high doses of haloperidol (CHAL, 5 mg/kg/day, s.c.) on midbrain dopamine (DA) neuronal activity. This regimen of HAL treatment produced a time-dependent reduction in the number of spontaneously active DA neurons. Additionally, this dose regimen induced an irregular firing pattern in many of the remaining active DA neurons in both the ventral tegmental area (A10) and substantia nigra pars compacta (A9) regions. These effects were comparable to those obtained previously in rats treated chronically with lower doses of HAL (0.5 mg/kg/day, s.c.). However, there was a greater decrease in the number of spontaneously active DA cells detected in rats treated with high doses of HAL for three weeks compared to those receiving the low doses. On the other hand, higher doses of apomorphine (200 micrograms/kg, i.v.) were required to reverse both the reduction of DA activity and irregular discharge pattern in rats treated chronically with high doses of HAL. In conclusion, the results of the present study substantiate the view that CHAL-induced depolarization inactivation (DI) of DA neurons is a time-dependent process and chronic treatment with high doses of HAL did not shorten the time course required for the development of DI on the majority of midbrain DA neurons.     

Effects of carvedilol and BL-443 on kidney of rats with cyclosporine nephropathy

Effects of cyclosporine A on kidneys of rats and the effects of carvedilol or BL-443 on kidneys of rats with cyclosporine nephropathy were studied. Male rats (Wistar) were divided into four groups (n = 7). Three groups of rats were treated in single oral daily doses of 45 mg cyclosporine A/kg body weight to cause cyclosporine nephropathy. Two of the treated groups were then medicated either with carvedilol or BL-443 in single daily doses of 10 mg/kg b.w., and 1 ml doses of saline were given daily i.p. to the third group of rats. Animals were treated and medicated for 17 days. The rats of intact group had no treatment and medication. L-lactate dehydrogenase isoenzymes LD(1-4) in the kidney extracts were determined by polyacrylamide gel clectrophoresis. Significant differences of LD(1-4) pattern in kidneys between intact rats and each of the three groups of rats with cyclosporine nephropathy were found by F-test and t-test (p < 0.05). Treatment with cyclosporine A affected the LD(1-4) pattern in kidneys. On the other hand, no significant differences of LD(1-4) pattern in kidneys between rats with non-treated cyclosporine nephropathy and rats with cyclosporine nephropathy medicated with carvedilol or BL-443 were found.     

Combined action of lead and lithium on essential and nonessential elements in rat blood

The effects of lead and lithium ingestion, separately and in combination, on the levels of K, Fe, Cu, Zn, Br, Rb, and As in rat blood were studied by the Energy Dispersive X-ray Fluorescence technique. Two different doses of lead acetate, i.e., 50 and 100 mg/Kg body wt (low and high doses), were administered orally to rats, daily, for 1 and 4 months (short and long terms), whereas lithium in the form of lithium carbonate was given to rats in food (1.1 g/kg diet) for 1 and 4 mo separately, and also to rats receiving lower and higher doses of lead. K levels were found to be depressed significantly with lead treatment, whereas Fe contents were enhanced marginally after 1 mo of treatment when only the higher dose of lead was given. As, Br, and Rb contents were found to be elevated following lead treatment for short and long terms at both the dose levels. However, Cu contents were lowered, whereas Zn contents were raised only after long term treatment with lead. The Fe, Cu, As, and Br contents remained unaltered, whereas K, Rb, and Zn contents were reduced significantly when lithium was administered for short term. Moreover, Cu and Fe levels were also found to be reduced and Br contents were enhanced only after long term treatment. During the combined treatment with lead and lithium for short and long terms, the levels of K, As, and Rb were observed to decrease, whereas Fe contents were enhanced when estimated for both doses of lead. On the contrary, Cu levels were lowered only with the higher dose of lead acetate when given in combination with lithium for 1 and 4 mo. Br contents were only effectively decreased after 4 mo of treatment.     

Effect of chronic D-fenfluramine administration on rat hypothalamic serotonin levels and release

D-fenfluramine, an anorectic agent in rats and man, was administered daily at doses 1.25, 2.5, 5 or 10 mg/kg/day for 10 days, and sacrificed 6 days later. Hypothalamic serotonin (5-HT) levels were unchanged in rats receiving 1.25-5 mg/kg/day of d-fenfluramine but reduced by 22% (p less than 0.01) at the highest drug dose (10 mg/kg/day); hypothalamic 5-hydroxyindole acetic acid (5-HIAA) levels were reduced by 15% (p less than 0.05) or 28% (p less than 0.01) in rats receiving 5 or 10 mg/kg/day of the drug, respectively. Hypothalamic slices prepared from rats which were previously treated with any of the drug doses spontaneously released endogenous 5-HT at rates that did not differ from those of vehicle-treated rats. 5-HT released with electrical field-stimulation was unaffected by prior d-fenfluramine treatment at doses of 1.25-5 mg/kg/day, and was reduced by 20% (p less than 0.05) from slices prepared from rats which received 10 mg/kg/day. 5-HIAA efflux was also attenuated by the highest drug dose. These data indicate that chronic administration to rats of customary anorectic doses of d-fenfluramine (i.e. 0.06-1.25 mg/kg) fail to cause long-lasting reductions in brain 5-HT release.     

Effects of Acute In vivo Cisplatin and Selenium Treatment on Hematological and Oxidative Stress Parameters in Red Blood Cells of Rats

Although cisplatin (cisPt) is one of the most often used cytotoxic drugs in the treatment of cancer, its clinical application is associated with nephrotoxicity and a cumulative anemia. In this study, we evaluated posible protective effects of selenium (Se) on hematological and oxidative stress parameters in rats, acutely treated with cisPt. Four groups of Wistar albino rats included control rats, cisPt-treated (7.5 mg/kg of body weight of cisPt, i.p.), Se-treated (6 mg/kg of body weight of Na₂SeO₄, i.p.), and Se and cisPt co-treated rats. The rats were killed 72 h after treatment; hematological and oxidative stress parameters were followed in red blood cells. The results showed depletion in platelet number induced by high acute doses of cisPt and strong utilization of reduced glutathione, resulting in elevation of GSSG/2 GSH ratio. Se treatment was followed by stimulated erythropoiesis, increased lipid peroxidation, and GSH depletion. Se and cisPt co-treatment were followed by stimulated erythropoiesis and significant recovery of reduced glutathione status when compared with cisPt-treated rats. In conclusion, acute doses of Se and cisPt primarily act as pro-oxidants. CisPt influenced antioxidative properties of exogenous Se and their synergistic effects may partially participate in protection against cisPt-induced toxicity.     

Aging alters gastric mucosal responses to epidermal growth factor and transforming growth factor-alpha

Administration of pharmacological doses of epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) in young rats stimulates gastric mucosal proliferation, but, in aged rats, the same treatment inhibits proliferation. This may be due to enhanced ligand-induced internalization of EGF receptor (EGFR). In support of this, we demonstrated that although a single injection of EGF (10 microg/kg) or TGF-alpha (5 microg/kg) in young (4-6 mo old) rats greatly increased membrane-associated EGFR tyrosine kinase activity, the same treatment slightly inhibited the enzyme activity in aged (24 mo old) rats. This treatment also produced a greater abundance of punctate cytoplasmic EGFR staining in gastric epithelium of aged rats, consistent with EGFR internalization. In vitro analyses demonstrated that exposure of isolated gastric mucosal cells from aged but not young rats to 100 pM TGF-alpha resulted in marked increases in intracellular EGFR tyrosine kinase activity and that induction of EGFR tyrosine kinase activity in mucosal membranes from aged rats occurred at doses 1,000-fold less than those required in young rats. Our data suggest that aging enhances sensitivity of the gastric mucosa to EGFR ligands. This may partly explain EGFR-mediated inhibition of gastric mucosal proliferation in aged rats.     

Vitamin D3 treatment regulates apoptosis,antioxidant defense system,and DNA integrity in the epididymal sperm of an aged rat model

The present study aimed to investigate the effects of vitamin D3 in the epididymal sperm cells of D ‐gal‐induced aged rats. It is well known that during aging sperm quality and quantity declines and leads to age‐related infertility problems in males. The results of the present study showed that there were elevated levels of oxidative stress and poor DNA integrity of sperm of aged rats. The expression of BCL2 also showed a significant decline in the sperm of aged rats, however, the expression of BAX and active caspase‐3 did not show significant change compared with the control group. The treatment of vitamin D3 at lower doses to aged rats showed increased expression of BAX and active caspase‐3 in the sperm, this finding suggests that increased apoptosis may be responsible for removal of poor quality sperm during aging. Vitamin D3 treatment at both doses showed improvement in the oxidative stress and DNA integrity in the sperm of aged rats. We also investigated the expression of AGER, visfatin, and HSPA1A in the epididymal sperm. It has been found that expression of AGER, visfatin, and HSPA1A increased in the sperm aged rats and vitamin D3 treatments at both doses decreased its expression. Thus, it might be suggested that during aging vitamin D3 treatment would be important for managing the sperm quality by regulating the apoptosis, antioxidant system and DNA integrity via modulation of visfatin and HSPA1A.     

Modulation of hepatic glucose-6-phosphate dehydrogenase activity in male and female rats by estrogen

The effect of estradiol-17 beta on the activity of glucose-6-phosphate dehydrogenase was studied in both male and female rats to further characterize the sex differences in the activity of this enzyme. Four groups of intact and castrated rats were implanted subcutaneously with graded doses (2.4, 4.8 and 7.2 micrograms/day) of pelleted estradiol in a physiologically relevant experimental system. After fourteen days the rats were sacrificed and their livers were assayed for G6PD activities. The result indicated that: (i) the enzyme activity was 3-fold higher in normal adult female than in male rats, (ii) low doses of E2 (2.4, 4.8 and 7.2 micrograms/day) increased the activity of G6PD 6-fold in castrated males and over 2-fold in female castrates as well as intact rats (iii) E2 stimulation of G6PD activity appears to be more effective in castrated males than in female rats (IV) sex difference in the activity of G6PD disappeared after treatment with E2 in castrated rats. It is concluded that the activity of G6PD in rats is markedly enhanced by low doses of E2, which appears to be largely responsible for the sex differences in the activity of this enzyme in rats.     

The effects of different steroids on costal and epiphyseal cartilage of fetal and adult rats

Summary The effects of different doses of various steroids on growth, and on costal and epiphyseal chondrocytes, have been studied in prenatal, immature, and adult Long-Evans rats using histochemical techniques, and both light and electron microscopy. Both prenatal and postnatal treatments have been employed. The steroids used were cortisone (CA), betamethasome (BM), and, in the prenatal group only, dexamethasone (DM).Body weight is reduced in all treated rats (except the low dose of CA) by day 17 of gestation, with greater weight reductions occurring in rats receiving the higher dose level of each steroid. In rats treated prenatally or neonatally, and sacrificed postnatally on days 39–43 or days 116–127, body weights, and tibial and tail lengths, are less than in correspondingly aged controls, thus showing a persistence of the effects of treatment.Costal and epiphyseal cartilages in prenatal rats show cellular, synthetic, and ultrastructural alterations induced by treatment with glucocorticoids but the responses are not necessarily comparable. Except for the low dose of DM, the higher doses of each steroid are more effective in inhibiting, or altering, growth and cellular differentiation in the developing fetuses. Surprisingly, a low dose of DM has a more devastating effect on the cells and extracellular matrix of both costal and epiphyseal cartilage, than do higher dose-levels of the various steroids. Low doses of CA and BM are also effective in inhibiting or altering growth and cellular differentiation, but their effectiveness is largely limited to 17 days of gestation. The order of effect of the various doses of the different steroids on fetal cartilage, listed in decreasing order of severity, is as follows: 0.12 DM, 0.24 DM, 0.42 BM, 50 CA, with 25 CA and 0.18 BM being approximately equal and only slightly different from control cartilages. The effect of prenatal or neonatal glucocorticoid treatment on chondrocytes is minimal in the 30–43 day, or 116–127 day, postnatal groups. In immature and adult rats, cortisone affects the chondrocytes more deleteriously than does betamethasone, and a 5.0 mg dose of CA seems to affect chondrocytes, body weight, and tibial and tail lengths more than 0.2 or 7.5 mg doses.Supported in part by NIH grant HD 07074 and HD 12034     

Antioxidative treatment of pregnant diabetic rats diminishes embryonic dysmorphogenesis

BACKGROUND: Diabetic pregnancy is still associated with an increased rate of congenital malformations despite extensive clinical efforts to normalize the risk for the offspring. The etiology of diabetic embryopathy is not clear; however, experimental studies have suggested a role for oxidative stress in the teratogenicity of diabetic pregnancy. The antioxidants alpha-tocopherol and ascorbate have improved fetal outcome in diabetic rodent pregnancy when supplemented in moderate to high doses. In the present work we investigated if extremely high doses of either alpha-tocopherol or ascorbate might further improve fetal outcome in offspring of diabetic rats and, in addition, if such treatment may exert any adverse effects of fetal development. METHODS: Nondiabetic and streptozotocin diabetic female rats were fed 2, 5, 10, or 15% alpha-tocopherol or 4, 10, or 15% ascorbate in their diet. RESULTS: Both alpha-tocopherol and ascorbate treatment improved fetal morphology in offspring of diabetic rats. There was a dose-dependent improvement for the alpha-tocopherol supplementation, in which the higher doses diminished fetal dysmorphogenesis more than the 2% diet. The ascorbate supplementation was less dose-dependent; however, the higher doses tended to improve fetal outcome more than the lower doses. No adverse effects of the antioxidants were noted in the offspring with the exception of 1 case of agnathia in a fetus of a nondiabetic rat supplemented with 15% alpha-tocopherol. CONCLUSIONS: These results indicate that very high doses of dietary antioxidants may be needed to normalize the development of the offspring in experimental diabetic pregnancy, but that treatment with such high doses may also have adverse effects in nondiabetic pregnancy.     

Opposing actions of dehydroepiandrosterone and corticosterone in rats.

The purpose of this study was to determine the impact of dehydroepiandrosterone (DHEA) and corticosterone (CORT) treatment, using implants as a route of administration, on specific hormones, metabolites, and enzymes involved in energy metabolism. Sixty male Sprague-Dawley rats, 325 g initial weight, were implanted subcutaneously for 3 weeks with time-release pellets containing either DHEA or CORT at doses of 0, 10, 25, 50, or 100 mg in this 2 x 5 factorial experiment. In general, body weights and food intakes decreased as the level of steroid hormones increased. In contrast to DHEA treatment, rats receiving the 50- and 100-mg doses of CORT had lighter thymus glands and spleens and heavier epididymal and retroperitoneal fat pads than their controls. Rats treated with 100 mg of DHEA had lowered serum levels of triglycerides and lipid hydroperoxides whereas rats treated with 100 mg of CORT had higher levels of these blood lipids compared to their respective controls. In contrast to DHEA treatment, there was a dose-dependent increase in liver lipid content and the specific activities of the hepatic lipogenic enzymes glucose-6-phosphate dehydrogenase, malic enzyme, and fatty acid synthase in response to CORT treatment. Rats treated with 100 mg of DHEA had higher serum levels of IGF-1 than control rats. Conversely, rats treated with 100 mg of CORT had lower serum levels of IGF-1 and higher serum levels of testosterone, progesterone, and insulin than their controls. These data demonstrate the lipogenic actions of corticosterone in rats. Conversely, DHEA treatment reduced serum and hepatic lipids. Furthermore, these data suggest that using implants instead of bolus injections of steroids may be a more physiological approach for studying the influence of these steroids on lipid metabolism.     

Effects of Milnacipran in Animal Models of Anxiety and Memory

Serotonin (5-HT) and noradrenaline (NA) are involved in both pathogenesis and recovery from depression and anxiety. We examined the effects of acute and chronic treatment with milnacipran, a serotonin/noradrenaline reuptake inhibitors (SNRIs) antidepressant, on anxiety and memory retention in rats. Male Wistar rats received acute or chronic administration of milnacipran (12.5, 25 or 50 mg/kg) or saline (control group). The animals were separately submitted to elevated plus-maze, inhibitory avoidance and open-field tasks 1 h after injection, in the acute group, or 23 h after last injection, in the chronic group. Our results showed an anxiolytic-like effect after chronic administration of milnacipran at doses of 25 and 50 mg/kg. The treatment does not interfere in memory retention and habituation to a novel environment at any doses studied. These findings support that milnacipran, an established SNRIs antidepressant, can also be useful in the treatment of anxiety disorders.     

Modification of the effect of fotrin in phenobarbital-induced metabolic system

Random bred male rats were given drinking water with phenobarbital (PB) (daily doses 0.4; 2 and 10 mg/kg) during 120 days. Activity of mixed function of oxygenases (content of cytochromes P-450) were enhanced after PB treatment in doses 2 and 10 mg/kg. Following PB treatment the animals were injected 5-times ethyleneimine derivate--fotrin at the doses 2, 4 and 7 mg/kg. The induction of mixed function of oxygenases resulted in significant decrease in the number of cells with chromosome aberrations.     

Decreased fructose concentrations in coagulating glands of prepuberal rats treated with testosterone and LH

Doses of testosterone propionate from 2.5 to 320 microgram and doses of LH from 2 to 360 microgram given over 1--3 days generally decreased fructose/body weight ratios in the coagulating glands of late prepuberal rats. The ratios of testes, seminal vesicles, coagulating glands and ventral prostates to body weight were increased after different treatment regimes with testosterone propionate. These changes in the variables measured could be detected by computer analysis in spite of the rapid growth rates of organs of rats of this age. LH increased the weights of only the seminal vesicles and coagulating glands, and then, only at the highest doses given.     

Further characterization of the direct inhibitory effect of LHRH agonists at the testicular level in the rat

To further clarify the relative importance of the pituitary and gonadal sites of LHRH action, intact and hypophysectomized adult male rats were treated with hCG for 7 days, in the presence or absence of simultaneous treatment with increasing doses of the LHRH agonist [D-Ser(TBU)6des-Gly-NH2(10)]LHRH ethylamide, Buserelin (0.025, 0.25, 2.5 or 25 micrograms/rat, twice daily). Daily treatment of intact adult rats with hCG (25 IU) markedly increased ventral prostate and seminal vesicle weight, while a dose-dependent inhibition of the effect was observed following combined administration of Buserelin. In hypophysectomized rats, treatment with hCG resulted in a partial restoration of ventral prostate and seminal vesicle weight, while combined treatment with a high dose of the LHRH agonist (25 micrograms, twice daily) partially (P less than 0.05) inhibited the stimulatory effect of hCG. LH/hCG receptors were almost completely inhibited after hCG injection alone and a further decrease was observed in the presence of simultaneous LHRH agonist treatment. The hCG-induced stimulation of GH/PRL receptors was counteracted by Buserelin treatment in hypophysectomized animals. The present data demonstrate that although LHRH-induced LH release has been shown to play a major role in the loss of testicular functions induced by low doses of LHRH agonists in the rat, a direct inhibitory action of LHRH agonists can be exerted at the testicular level at high doses of the peptide.