Effects of chronic alternating cadmium exposure on the episodic secretion of prolactin in male rats.

Cadmium increases or decreases prolactin secretion depending on the dose and duration of the exposure to the metal. However, whether there are cadmium effects on the episodic prolactin secretion is less well known. This study was undertaken to address whether chronic alternating exposure to two different doses of cadmium affects the episodic pattern of prolactin and to what extent the effects of cadmium are age-dependent. Male rats were treated s.c. with cadmium chloride (0.5 or 1.0 mg/kg) from day 30 to 60, or from day 60 to 90 of age, with alteration of the doses every 4 days, starting with the smaller dose. Controls received vehicle every 4 days. The last dose of cadmium was given 48 h prior to the pulsatility study. Prolactin secretion in the 4 experimental groups studied was episodic and changed significantly after cadmium exposure. Cadmium administration from day 30 to 60 of life significantly decreased the mean half-life of prolactin. On the other hand, when administered from day 60 to 90 cadmium significantly decreased the mean as well as serum prolactin levels and the absolute amplitude of the prolactin pulses, their duration, the relative amplitude or the mean half-life of the hormone. The frequency of prolactin peaks was not changed by cadmium administration. The results indicate that low intermittent doses of cadmium chronically administered change the episodic secretion pattern of prolactin in rats. The effects of cadmium on prolactin secretion were age dependent.     

Cadmium chronotoxicity at pituitary level: effects on plasma ACTH,GH, and TSH daily pattern

Cadmium is an endocrine disruptor that has been shown to induce chronotoxic effects. The present study was designed to evaluate the possible cadmium effects on the daily secretory pattern of adrenocorticotropin hormone (ACTH), growth hormone (GH), and thyroid-stimulating hormone (TSH) in adult male Sprague-Dawley rats. For this purpose, animals were treated with cadmium at two different doses [25 and 50 mg/l cadmium chloride (CdCl₂)] in the drinking water for 30 days. Control age-matched rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24-h cycle. Cadmium exposure modified the 24-h pattern of plasma ACTH and GH levels, as the peak of ACTH content between 12:00 and 16:00 h in controls appeared at 12:00 h in the group treated with the lowest dose used, while it appeared between 16:00 and 20:00 h in rats exposed to 50 mg/l CdCl₂. In addition, the peak of GH content found at 04:00 h in controls moved to 16:00 h in rats exposed to 25 mg/l CdCl₂, and the highest dose used abolished 24-h changes of GH secretion. The metal treatment did not modify ACTH secretory pattern. Exposure to cadmium also increased ACTH and TSH medium levels around the clock with both doses used. These results suggest that cadmium modifies ACTH and TSH medium levels around the clock, as well as disrupted ACTH and GH secretory pattern, thus confirming the metal chronotoxicity at pituitary level.     

Are cadmium effects on plasma gonadotropins, prolactin, ACTH, GH and TSH levels, dose-dependent?

It is well established that cadmium affects plasma levels of the pituitary hormones studied. However, whether the effects of the metal are dose dependent needs to be clarify. This work was designed to evaluate the possible changes in plasma levels of gonadotropins, prolactin, ACTH, GH and TSH after oral cadmium exposure in adult male rats. Plasma levels of these hormones were measured in adult male rats exposed to cadmium chloride (CdCl₂) in the drinking water at the doses of 5, 10, 25, 50 or 100 ppm for one month. The lower dose of cadmium increased plasma prolactin levels and higher doses of the metal (25 or 50 ppm) decreased them. There was a continuous increase of plasma ACTH levels from the lower to 25 ppm dose of CdCl₂ and decreased them after to basal values with the highest dose. Plasma GH levels were increased with the dose of cadmium of 10 ppm, although the doses of 5, 25 and 50 ppm decreased them. Plasma LH levels were only reduced with the dose of 50 ppm of CdCl₂, whereas those of FSH increased. Plasma TSH levels were increased with the doses of 5, 25 and 100 ppm of CdCl₂. Cadmium concentration increased in pituitary with the doses of 125, 50 and 100 ppm of CdCl₂. These data suggest that cadmium differentially affects the secretory mechanisms of the pituitary hormones studied depending on the dose used. The effects of the metal on prolactin and ACTH are dose-dependent.     

Effects of subchronic alternating cadmium exposure on dopamine turnover and plasma levels of prolactin, GH and ACTH

This study was undertaken to analyze if the effects of subchronic alternating cadmium exposure on pituitary hormone secretion are mediated by changes in dopamine turnover in an age dependent way or are directly correlated to cadmium accumulation at the hypothalamic-pituitary axis. Male rats were treated sc. from day 30 to 60 (prepubertal period) or from day 60 to 90 (adult age) of life, with cadmium chloride (CdCl₂) at a dose of 0.5 and 1.0 mg kg^–1 bw, every 4th day in an alternate schedule, starting with the smaller dose. Dopamine (DA) turnover, expressed as the ratio of acid 3,3-dihidroxifenil acetic (DOPAC)/DA in various hypothalamic areas, the plasma levels of prolactin, growth hormone (GH) and adrenocorticotropic hormone (ACTH), and cadmium accumulation in the hypothalamus and pituitary were studied. Prepubertal cadmium exposure decreased DA content in all hypothalamic areas studied, although its turnover was not modified. A decrease in plasma ACTH levels with no changes in plasma prolactin and GH levels were found. Cadmium did not accumulate in pituitary while it increased in the hypothalamus. Metal exposure during adulthood decreased DA content in mediobasal and posterior hypothalamus, and its turnover in posterior hypothalamus and median eminence. It decreased plasma prolactin and ACTH levels but not those of GH. Cadmium concentration increased in both hypothalamus and pituitary. These results suggest that cadmium exposure produces age dependent changes on the secretory mechanisms of the pituitary hormones studied, related to the selective accumulation of the metal at both hypothalamic and hypophyseal level changes. However the effects of the metal are not mediated by dopamine.     

Cadmium toxicity and liver mitochondria. I. Different effects of cadmium administered in vivo to adult, young, and ethionine-fed rats

The changes in liver mitochondrial respiratory activities and cytochrome concentrations were investigated when cadmium chloride was administered orally to adult, young, and ethionine-fed rats. Following a seven-day administration of 30 ppm cadmium in drinking water, adult rats showed no change, while young rats and ethionine-fed rats exhibited a marked increase in mitochondrial respiration with concomitant decrease of respiratory control index and P/O ratio. The concentrations of cytochromes aa3, b, and c + c1 in liver mitochondria were unchanged in adult rats, but increased significantly in ethionine-fed rats. In young rats receiving cadmium the liver mitochondrial protein increased with a slight change in the cytochrome concentration in mitochondria. It was further found that in adult rats a higher concentration (300 ppm) of cadmium in drinking water was toxic to the liver mitochondrial functions. Thus, the effect of oral administration of cadmium on the liver mitochondrial function depends on the condition of the animals.     

Effect of dexamethasone on steroidogenesis and on adrenocortical cyclic AMP and cyclic GMP responses to ACTH

The inhibitory action of dexamethasone on the adrenal steroidogenic response to ACTH was confirmed by im administration of graded doses (5, 10 and 30 ng) of synthetic beta 1-24 ACTH to young adult male rats which had received dexamethasone (0.1 mg/100 g bw) 4 hr prior to sacrifice. Following this, kinetic studies were performed by measuring plasma corticosterone, adrenocortical cyclic AMP and cyclic GMP before and 4, 12 and 30 min after administration of either 10 or 30 ng of ACTH. These doses were selected because their effects could be either completely or partially inhibited by dexamethasone. In rats without dexamethasone all the doses of ACTH which were checked induced an increase in both corticosterone and cyclic AMP and a decrease in cyclic GMP. With the smallest dose of ACTH the earlier administration of dexamethasone resulted in complete suppression of both the steroidogenic response and the cyclic AMP response. With the largest dose of ACTH both responses were diminished. In dexamethasone-treated rats the decrease in cyclic GMP was significantly less pronounced 4 min after ACTH than it was in non-treated rats. These results support the view that cyclic AMP and cyclic GMP might both be concerned with the mechanism of acute adrenal steroidogenesis.     

Cadmium does not inhibit pulsatile prolactin secretion through TRH

This work was undertaken to analyse the effects of acutecadmium administration on the pulsatile patternof prolactin release, in adult male rats.For this purpose, animals were cannulated 40 h before the experi-mentto allow a continuousblood withdrawal. Two hours after the administration of one dose of cadmiumchloride (4.5 mg kg1 ), the pulsatile pattern of prolactin, during three hours, was studied. The effects oftwopulses of thyrotropin-releasing hormone (TRH) (1 mg per rat), given 60 and 120 min afterstarting the periodof blood sampling, were studied. The mean values of prolactin during thebleeding period and the absolutepulse amplitude were decreased by acute cadmium chlorideadministration. However, no changes in anyother parameters of prolactin pulsatility were observed.TRH administration to control rats increased meanprolactin levels, and absolute andrelative pulse amplitudes, but decreased the mean half-life of the hormone.In animals pretreated withcadmium, TRH increased the mean levels of prolatin, and absolute and relativeamplitudes ofthe hormone pulses. No other parameter studied was changed by TRH in cadmiumpretreatedrats. These data suggest that acute administration of cadmium did not inhibit thepulsatile prolactin releasethrough TRH.     

Oxytocin inhibits ACTH and peripheral catecholamine secretion in the urethane-anesthetized rat

Oxytocin (OT) generally has a stimulatory effect on ACTH secretion both in vitro and in vivo. As part of a study of ACTH-releasing factors in hypophysial portal blood, the effects of i.v. OT administration on plasma ACTH levels were tested in urethane-anesthetized rats. Surprisingly, i.v. injection of 10 micrograms OT lowered plasma ACTH levels by about 35% (P less than 0.01). It was reasoned that this paradoxical inhibition of ACTH secretion by OT might be mediated by inhibition of the unusually high rate of peripheral catecholamine secretion in this model. Measurement of plasma catecholamines before and after i.v. administration of 10 micrograms OT revealed a 53% inhibition of EPI (P less than 0.01) and 43% inhibition of NE (P less than 0.05). Administration of the beta-adrenergic antagonist propranolol (400 micrograms) 15 min before the beginning of the experiment completely blocked the inhibitory effects of OT on ACTH secretion and in fact unmasked the stimulatory effects of OT normally seen in conscious animals and in vitro. Superfused bisected adrenal glands exposed to 10(-6) M OT for 10 min secreted more than 30% less EPI and NE than control adrenals suggesting that the inhibition of EPI and NE secretion by OT in vivo occurs, at least in part, directly at the level of the adrenal. The data support the hypothesis that peripheral catecholamines may at times be directly involved in the control of ACTH secretion and also suggest that OT, which has recently been identified in the adrenal medulla, may have important paracrine functions in the regulation of adrenal catecholamine secretion.     

Interactions between oxytocin, glucagon and glucose in normal and streptozotocin-induced diabetic rats

Oxytocin has been suggested to have glucoregulatory functions in rats, man and other mammals. The hyperglycemic actions of oxytocin are believed to be mediated indirectly through changes in pancreatic function. The present study examined the interaction between glucose and oxytocin in normal and streptozotocin (STZ)-induced diabetic rats, under basal conditions and after injections of oxytocin. Plasma glucose and endogenous oxytocin levels were significantly correlated in cannulated lactating rats (r = 0.44, P less than 0.01). To test the hypothesis that oxytocin was acting to elevate plasma glucose, adult male rats were injected with 10 micrograms/kg oxytocin and killed 60 min later. Oxytocin increased plasma glucose from 6.1 +/- 0.1 to 6.8 +/- 0.2 mM (P less than 0.05), and glucagon from 179 +/- 12 to 259 +/- 32 pg/ml (P less than 0.01, n = 18). There was no significant effect of oxytocin on plasma insulin, although the levels were increased by 30%. A lower dose (1 microgram/kg) of oxytocin had no significant effect on plasma glucose or glucagon. To eliminate putative local inhibitory effects of insulin on glucagon secretion, male rats were made diabetic by i.p. injection of 100 mg/kg STZ, which increased glucose to greater than 18 mM and glucagon to 249 +/- 25 pg/ml (P less than 0.05). In these rats, 10 micrograms/kg oxytocin failed to further increase plasma glucose, but caused a much greater increase in glucagon (to 828 +/- 248 pg/ml) and also increased plasma ACTH. A specific oxytocin analog, Thr4,Gly7-oxytocin, mimicked the effect of oxytocin on glucagon secretion in diabetic rats. The lower dose of oxytocin also increased glucagon levels (to 1300 +/- 250 pg/ml), but the effect was not significant. A 3 h i.v. infusion of 1 nmol/kg per h oxytocin in conscious male rats significantly increased glucagon levels by 30 min in normal and STZ-rats; levels returned to baseline by 30 min after stopping the infusion. Plasma glucose increased in the normal, but not STZ-rats. The relative magnitude of the increase in glucagon was identical for normal and diabetic rats, but the absolute levels of glucagon during the infusion were twice as high in the diabetics. To test whether hypoglycemia could elevate plasma levels of oxytocin, male rats were injected i.p. with insulin and killed from 15-180 min later. Plasma glucose levels dropped to less than 2.5 mM by 15 min. Oxytocin levels increased by 150-200% at 30 min; however, the effect was not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)     

Interaction of GnRH agonists, pituitary hormones and corticosteroids on progesterone secretion in the male rat

The effect of the GnRH superagonist [D-Trp⁶, Pro⁹-NEt]-GnRH (SA) and ACTH on progesterone (P_o) secretion was compared in intact, adrenalectomized (ADX), castrated (CST) or hypophysectomized (hypox) adult male rats. SA increased circulating gonadal plasma P_o levels only, while ACTH acted on the adrenal secretion of this steroid, but not the gonadal one. The concomitant administration of dexamethasone partially inhibited the SA-induced increase in gonadal P_o production. SA did not modify plasma P_o levels in hypox rats. By contrast, ACTH did not require the presence of the pituitary to stimulate P_o secretion. This data indicates that adrenal steroids may modulate some of the effects of GnRH and its agonists on the testes.     

Possible role of glutamate, aspartate, glutamine, GABA or taurine on cadmium toxicity on the hypothalamic pituitary axis activity in adult male rats

This work was designed to evaluate the possible changes in glutamate, aspartate, glutamine, GABA and taurine within various hypothalamic areas the striatum and prefrontal cortex after oral cadmium exposure in adult male rats, and if these changes are related to pituitary hormone secretion. The contents of glutamine, glutamate, aspartate, GABA and taurine in the median eminence, anterior, mediobasal and posterior hypothalamus, and in prefrontal cortex in adult male rats exposed to 272.7 mol l^–1 of cadmium chloride (CdCl₂) in the drinking water for one month. Cadmium diminished the content of glutamine, glutamate and aspartate in anterior hypothalamus as compared to the values found in the untreated group. Besides, there is a decrease in the content of glutamate, aspartate and taurine in the prefrontal cortex. The amino acids studied did not change in median eminence, mediobasal and posterior hypothalamus or the striatum by cadmium treatment. Plasma prolactin and LH levels decreased in rats exposed to the metal. These results suggest that (1) cadmium differentially affects amino acid content within the brain region studied and (2) the inhibitory effect of cadmium on prolactin and LH secretion may be partially explained by a decrease in the content of both glutamate and aspartate in anterior hypothalamus, but not through changes in GABA and taurine.     

Daily pattern of pituitary glutamine, glutamate, and aspartate content disrupted by cadmium exposure

Cadmium is a neurotoxic heavy metal and is considered endocrine disruptor. In this work, we investigate the effects of cadmium on the 24 h changes of aspartate, glutamate, and glutamine content in the pituitary. Adult male Sprague–Dawley rats were treated with 25 or 50 mg/l of cadmium chloride (CdCl₂) in the drinking water for 30 days. Metal exposure with the lowest dose induced the disappearance of the nocturnal peak of anterior pituitary amino acid content, and the appearance of a peak of glutamine concentration during the resting phase of the photoperiod. After exposure to 50 mg/l of CdCl₂, the peaks of anterior pituitary amino acid content at 12:00 and 00:00 h disappeared, and two minimal values at these same hours and a peak at 08:00 h appeared. In the posterior pituitary, cadmium treatment with the lowest dose induced the appearance of a peak of aspartate and glutamate concentration at 12:00 h, and the disappearance of the peak of glutamine content at 16:00 h. After exposure to 50 mg/l of CdCl₂ aspartate and glutamate daily pattern presented two maximal values between 00:00 and 04:00 h, and the metal abolished glutamine daily pattern. These results suggest that cadmium disrupted aspartate, glutamate, and glutamine daily pattern in the pituitary.     

Suppression of luteinizing hormone and testosterone secretion in bulls following adrenocorticotropin hormone treatment

The present investigation was conducted to evaluate the inhibitory effects of adrenal corticosteroids on testosterone production by the bull testis. Administration of a single i.v. dose of adrenocorticotropic hormone (ACTH; 80 IU) resulted in a corticosteroid peak which lasted approximately 6 h. During this 6 h period, no episodic increases in secretion of LH or testosterone were initiated and basal concentrations of testosterone were suppressed (P less than 0.05) below control values. Episodic secretion of LH and testosterone resumed 6--7 h after ACTH when concentrations of serum corticosteroids had returned to basal levels. These results suggest that ACTH-induced increases in serum corticosteroids suppress the episodic secretion of LH, resulting in a suppression of testosterone secretion by the bull testis.     

Strain difference in pituitary-adrenal axis between Wistar-Imamichi and Long Evans adult male rats.

In the present study, we used closed colony-Wistar-Imamichi (WI), inbred WI and Long Evans (LE) adult male rats to examine the secretion of ACTH and corticosterone in response to restraint stress. Blood (0.3 ml) was withdrawn through a jugular cannula at 0, 15, 30, 60 and 120 min after the onset of restraint stress. Plasma concentrations of ACTH and corticosterone increased after stress in all groups, but the responses of ACTH and corticosterone secretion were higher in LE rats than in WI rats. Present data suggest that the LE rat might be a good model as a high-response strain and the closed colony or the inbred WI rat might be a good model as a low-response strain in restraint stress experiments.     

Changes in mean plasma ACTH reflect changes in amplitude and frequency of secretory pulses

ACTH is secreted in an episodic manner from the anterior pituitary. Unanesthetized rats with indwelling jugular and femoral venous cannulae were continuously bled and simultaneously infused with isotonic fluid by peristaltic pump. Two-minute blood samples were collected for up to five hours in 8 male rats. ACTH was measured by radioimmunoassay. The resulting time series were analyzed for significant secretory pulses with the PULSAR program. Elevations or declines in mean plasma ACTH levels were associated with significant changes in amplitude and frequency of secretory pulses.     

Effects of pretreatment with adrenocorticotropin on endocrine and behavioral responses of bulls to sexual activity

Peripheral concentrations of cortisol, growth hormone and testosterone were determined in two experiments which examined the endocrine and behavioral responses of sexually mature Angus bulls to an estrous female (Experiment 1) and to female exposure 5 hours following an adrenocorticotropin (ACTH) injection (Experiment 2). Sexual activity of bulls in Experiment 1 significantly increased levels of cortisol when compared with concentrations before exposure to a female. Administration of ACTH in Experiment 2 consistently elevated levels of cortisol by 30-fold (P<0.01) when compared with pre-ACTH concentrations. This heightened level of cortisol persisted throughout the period of exposure to an estrous cow, although a gradual decline in cortisol concentrations occurred over time (P<0.05). In Experiment 1, growth hormone profiles tended to increase in response to sexual activity (P<0.10), whereas in Experiment 2, growth hormone increased in response to ACTH administration (P<0.01) and to female exposure (P<0.01). Concentrations of testosterone were unaffected (P>0.10) by mating activity in Experiment 1. In Experiment 2, acute suppression (P<0.01) in testosterone concentrations 5 hours after ACTH administration coincided with the exposure period to the estrous female. Frequencies of mounting behavious (penis extension, mounting, intromission and ejaculation) exhibited by ACTH-treated bulls were significantly lower compared with the frequencies two days earlier. Exogenous ACTH administration suppressed reproductive behaviors of bulls and altered secretion of cortisol, growth hormone and testosterone. Furthermore, these data provide evidence that specific mating behaviors of the bull can be influenced by circulating steroids.     

Effects of metal cations on pituitary hormone secretion in vitro

Increased body burdens of metal cations are known to affect adversely reproductive function in several species. The effects of these metals on gonadal function are well documented. In contrast, little is known about their possible direct effects on pituitary hormone release. The purpose of this study was to determine, in vitro, the effects of nickel, cadmium, and zinc (50 μM) on both baseline and potassium chloride (KCl)-stimulated pituitary luteinizing hormone (LH), prolactin (Prl), and thyroid-stimulating hormone (TSH) release. Anterior pituitary fragments from adult male Long-Evans rats were evaluated using a continuous-flow perifusion system. Baseline and stimulated LH releases were unaffected by nickel and zinc; however, cadmium caused an increase in baseline LH secretion. Baseline Prl release was decreased by zinc, while cadmium resulted in increased release of this hormone. Stimulated Prl release was lower during exposure to zinc but unaltered by nickel and cadmium. Following exposure to zinc, a rebound in stimulated release was noted for all three hormones measured. These results showed that the metal cations tested did have a direct effect on pituitary hormone release at a dose lower than those reported to alter testicular function in vitro. Furthermore, the changes in pituitary hormone secretion varied depending upon the metal and hormone being evaluated.     

Pulsatile ACTH secretion: variation with time of day and relationship to cortisol

It has long been known that ACTH is secreted in an episodic fashion demonstrating circadian and ultradian rhythms. High intensity venous sampling has recently revealed that in addition to these larger ultradian fluctuations in hormone levels, plasma ACTH in rats demonstrates high frequency, low amplitude oscillations which have been called "micropulses." These micropulses were not detected in previous studies due to sampling intervals of greater than 5 minutes. To investigate the presence of these ACTH micropulses in a primate species, blood samples were drawn from six chair-restrained rhesus monkeys at one-minute intervals for up to 70 minutes and plasma was assayed for immunoreactive ACTH. To assess the variation in ACTH micropulse parameters with time of day and the relationship to cortisol secretion, four of the monkeys were sampled for three 70-minute periods beginning at 0530, 1100, and 1730 hours, and plasma was assayed for immunoreactive ACTH and cortisol. Analysis of the data revealed that ACTH and cortisol are secreted in micropulses in rhesus monkeys with marked individual variation in the pattern of secretion and a concurrence of approximately 75% of ACTH and cortisol micropulses. Difference in pulse amplitude but not frequency appeared to contribute to the circadian variation in mean ACTH levels and a sampling interval of two minutes appeared to be adequate for accurately identifying micropulses of ACTH.     

Effects of maternal deprivation on adrenal and behavioural responses in rats with anterodorsal thalami nuclei lesions

There is evidence that repeated maternal isolation of neonatal rats may influence both emotional behavior and Hypothalamic-Pituitary Adrenal (HPA) activity. On the other hand the Anterodorsal Thalami Nuclei (ADTN) exerts an inhibitory influence on the hypophyso-adrenal system under basal and stressful conditions. In the present work we investigated whether neonatal maternal deprivation produces long term effects on the ADTN regulation of behavioral patterns (open field test) and on HPA axis activity. Specifically, we sought to determine whether adult female rats with ADTN lesions, previously isolated for 4.5 hours daily during the first 3 weeks of life, react in endocrinologically and behaviourally distinct manner as compared to controls. The examined groups were: non maternally deprived (NMD)/sham lesioned, NMD/lesioned, maternally deprived (MD)/sham lesioned, MD/lesioned with and without the open field test. At 3 months MD/sham lesioned animals showed a marked decrease in ambulation (P < 0.01), and with ADTN lesion, the rearing values were lower (P < 0.01) and grooming higher (P < 0.05) than NMD. This last data would indicate a high emotional index. Regarding the activity of the HPA axis, maternal deprivation induced a significant decrease in plasma ACTH concentration both in sham and lesioned animals (P < 0.001), and plasma Corticosterone (C) increased in sham animals (P < 0.001). This data would indicate a higher sensitivity of the adrenal glands. After the open field test ACTH and C were different between deprived and non-deprived animals depending on the ADTN lesion. Taking into consideration the increase of ACTH levels in sham lesioned MD animals exposed to the test, we could conclude that this new situation was a stressful situation. Finally in the present work, it was very difficult to relate the behavioral parameters with the endocrine data. It is known that depending on the context, corticosteroids may produce opposite effects on emotional behavior via different receptors in the brain.In summary, neonatal maternal deprivation induced alterations of behavioral patterns and affected the ADTN inhibitory influence on ACTH and C secretion.     

Modulation of adrenal cell functions by cadmium salts. 1. Cadmium chloride effects on basal and ACTH-stimulated steroidogenesis

Cultured Y-1 mouse adrenal tumor cells, which secrete 20--hydroxy-4-pregnen-3-one (20-DHP), were used to investigate the acute nonlethal effects of incremental cadmium chloride (CdCl₂) concentrations on basal and maximally stimulated steroid secretion. In addition, cumulative CdCl₂ effects during 4-hr incubations, effect reversibility, and viability were determined. Cells were incubated in 1 ml serum-free Eagle's Minimal Essential Medium (FMEM) with or without 0.5 IU (ca. 1.5 M) adrenocorticotropin (ACTH) in the presence or absence of CdCl₂. Following incubation, cell viability was quantitated using trypan blue exclusion. The 20-DHP secreted into the experimental incubation medium was measured by radioimmunoassay. CdCl₂ levels of 10.0 g/ml or greater significantly inhibited basal 30 min steroid secretion in a dose-dependent manner; ACTH-stimulated steroid secretion was significantly inhibited by levels 5.0 g/ml or greater. At least 80% of all control and stimulated cells in the presence or absence of cadmium ions excluded trypan blue. The reduction in ACTH-stimulated steroid secretion was greater than the reduction in basal steroid secretion at any cadmium concentration level. The CdCl₂ concentration that reduced stimulated steroid hormone secretion by 50% (IC₅₀) was 45.0 g/ml. Exposing Y-1 cells to either 5.0, 10.0, 45.0 or 500.0 g CdCl₂/ml FMEM for periods ranging from 0.5 to 4 hr inhibited ACTH-stimulated steroid secretion in a time-dependent manner. After 30 min exposure to 10.0, 45.0 or 500.0 g CdCl₂/ml FMEM with or without ACTH, cadmium inhibition was irreversible. When 5.0 g CdCl₂/ml was used, basal and stimulated inhibition was reversible by reincubating in medium containing ACTH alone. The relatively greater cadmium effects on ACTH stimulated steroidogenesis might suggest that cadmium modulated the rate-limited transducing system between the ACTH plasma membrane receptor complex and cholesterol side-chain cleaving mitochondrial enzymes. However, cadmium influences on basal secretion indicated effects on the non-rate-limited steroidogenic pathway.Abbreviations ACTH adrenocorticotropin - ANOVA analysis of variance - CdCl₂ cadmium chloride - Ci Curie - DNA deoxyribonucleic acid - FMEM serum-free Eagle's Minimum Essential Medium - HEPES N-2-hydroxyethylpiperazine-N-1,2-ethanesulfonic acid - IC₅₀ concentration inhibiting stimulated steroid secretion by 50% - IU international unit - MEM Eagle's Minimum Essential Medium - RIA radioimmunoassay - RNA ribonucleic acid - SEM standard error of the mean - SMEM serum-containing Eagle's Minimum Essential Medium - 20-DHP 20--hydroxy-4-pregnen-3-one