Invited review: Adrenocortical function in avian and non-avian reptiles: Insights from dispersed adrenocortical cells

Herein we review our work involving dispersed adrenocortical cells from several lizard species: the Eastern Fence Lizard (Sceloporus undulatus), Yarrow's Spiny Lizard (Sceloporus jarrovii), Striped Plateau Lizard (Sceloporus virgatus) and the Yucatán Banded Gecko (Coleonyx elegans). Early work demonstrated changes in steroidogenic function of adrenocortical cells derived from adult S. undulatus associated with seasonal interactions with sex. However, new information suggests that both sexes operate within the same steroidogenic budget over season. The observed sex effect was further explored in orchiectomized and ovariectomized lizards, some supported with exogenous testosterone. Overall, a suppressive effect of testosterone was evident, especially in cells from C. elegans. Life stage added to this complex picture of adrenal steroidogenic function. This was evident when sexually mature and immature Sceloporus lizards were subjected to a nutritional stressor, cricket restriction/deprivation. There were divergent patterns of corticosterone, aldosterone, and progesterone responses and associated sensitivities of each to corticotropin (ACTH). Finally, we provide strong evidence that there are multiple, labile subpopulations of adrenocortical cells. We conclude that the rapid (days) remodeling of adrenocortical steroidogenic function through fluctuating cell subpopulations drives the circulating corticosteroid profile of Sceloporus lizard species. Interestingly, progesterone and aldosterone may be more important with corticosterone serving as essential supportive background. In the wild, the flux in adrenocortical cell subpopulations may be adversely susceptible to climate-change related disruptions in food sources and to xenobiotic/endocrine-disrupting chemicals. We urge further studies using native lizard species as bioindicators of local pollutants and as models to examine the broader eco-exposome.

Modulation of adrenal steroidogenesis by testosterone in the lizard, Coleonyx elegans

Our previous work with adrenocortical cells from several Sceloporus lizard species suggests that gonadal hormones influence the steroidogenic capacity and the sensitivity to ACTH. However, there are discrepancies in these cellular response parameters suggesting that the effects of gonadal hormones on adrenocortical function vary with species, sex, age, season, and environmental/experimental conditions. To gain further insight into these complex interactions, here we report studies on Coleonyx elegans, Eublepharidae (Yucatán Banded Gecko), which is only distantly related to Sceloporus lizards via a basal common ancestor and in captivity, reproduces throughout the year. We hypothesized that a more constant reproductive pattern would result in less variable effects of gonadal hormones on adrenocortical function. Reproductively mature male geckos were orchiectomized with and without replacement of testosterone (300 μg) via an implanted Silastic® tube. Reproductively mature intact female geckos received implants with and without testosterone. After 11 weeks, adrenocortical cells were isolated from these lizards and incubated with corticotropin (ACTH) for 3 h at 28 °C. Three adrenocortical steroids, progesterone, corticosterone and aldosterone, were measured by highly specific radioimmunoassays. The production rate of each steroid was statistically analyzed using established software and net maximal rate (by subtracting the basal rate) in response to ACTH was determined. In general, corticosterone predominated and comprised ∼83% of the total net maximal rate, followed by progesterone (∼14%) and aldosterone (∼3%). Compared to the functional responses of adrenocortical cells derived from other lizards thus far, adrenocortical cells from C. elegans exhibited a depressed steroid response to ACTH and this depressed response was more pronounced in male cells. In addition, other sex differences in cellular response were apparent. In female cells, the net maximal rates of progesterone, corticosterone and aldosterone were, respectively, 161, 122 and 900% greater than those in intact-male cells. In contrast, cellular sensitivity to ACTH, as determined by the half-maximally effective steroidogenic concentration (EC₅₀) of ACTH, did not differ between intact-male and intact-female adrenocortical cells. Treatment effects were most striking for corticosterone, the putative, major glucocorticoid in lizards. Orchiectomy caused an increase in the net maximal corticosterone rate equivalent to that of intact-female cells. Testosterone maintenance in orchiectomized lizards completely suppressed the stimulatory effect of orchiectomy. However, orchiectomy with or without testosterone maintenance did not alter cellular sensitivity to ACTH. The effect of testosterone supplementation in intact females, although suppressive, was notably different from its effect in orchiectomized males. Its effect on the net maximal corticosterone rate was relatively modest and did not completely "masculinize" the greater rate seen in intact-female cells. However, testosterone supplementation dramatically suppressed the basal corticosterone rate (by 82%) and enhanced the overall cellular sensitivity to ACTH by 150%, two effects not seen in cells derived from testosterone-treated orchiectomized lizards. Collectively, these findings clearly indicating that the gonad directly or indirectly regulates lizard adrenocortical cell function. Whereas other gonadal or extra-gonadal factors may play a role, testosterone appears to be an essential determinant of the observed sex differences in adrenocortical function.

Effects of food restriction on steroidogenesis in dispersed adrenocortical cells from Yarrow's Spiny Lizard (Sceloporus jarrovii)

Changes in energy balance can lead to functional alterations at all levels of the hypothalamic-pituitary-adrenal (HPA) axis. However, relatively little is known about how energy balance affects functional properties of adrenocortical cells themselves. We investigated effects of restricted food intake on sensitivity to ACTH and rates of steroidogenesis in adrenocortical cells isolated from growing female and male Yarrow's Spiny Lizards (Sceloporus jarrovii). At the end of the feeding regimen, we assayed acute (3h) progesterone (P(4)), corticosterone (B), and aldosterone (ALDO) production in response to ACTH in dispersed adrenocortical cells. Food restriction depressed growth rate by about 50% in both males and females but did not alter baseline plasma B measured at 10 weeks in either sex. At the cellular level, food restriction had the following effects: (1) increased basal B production in both sexes and basal ALDO production in males, (2) increased net maximal rates of production of P(4), B, and ALDO in response to ACTH, and (3) no overall effect on adrenocortical cellular sensitivity to ACTH. There were modest sex differences: overall rates of P(4) production were 46% greater in cells from females than from males, and in response to food restriction, the net maximal rate of ALDO production was 50% greater in cells from males than from females. Our results demonstrate that food restriction in S. jarrovii increases adrenocortical cellular rates of steroid production without affecting overall cellular sensitivity to ACTH.

Long-term dietary lipid regimen alters adrenocortical function at the cellular level

Evidence indicates that dietary lipids influence adrenocortical function. In the present study, weanling rats were fed isocaloric synthetic diets for 6 and 12 months that contained 10% of one of the selected fatty acids as the predominant lipid: butter fat (high saturated, low polyunsaturated fat); olive oil (monounsaturated); corn oil (polyunsaturated); omega-3 ethyl ester mixture (long-chain polyunsaturates); elevated eicosapentaenoic acid; elevated docosahexaenoic acid. Adrenocortical cells derived from individual rats were evaluated for corticosterone and aldosterone responses to adrenocorticotropic hormone (ACTH). All comparisons were to the butter fat diet. Adrenocortical cell sensitivity to ACTH was not affected by the diets. However, there were differences in basal and maximal ACTH-induced corticosteroid production. Compared to the butter fat diet, the other diets variably decreased cellular corticosteroid production. Corticosterone and aldosterone production were affected similarly. The greatest decrease was most often seen with the omega-3 mixture diet (about -67%). At 6 months, the docosahexaenoic acid-elevated diet had selective suppressive actions on adrenocortical function whereas at 12 months, both docosahexaenoic and eicosahexaenoic acid-elevated diets had similar suppressive efficacies. The data indicate that a diet rich in high saturated, low polyunsaturated fat augments adrenocortical function and increasing the representation of long-chain unsaturated fatty acids suppresses adrenocortical function.

Gonadal modulation of in vitro steroidogenic properties of dispersed adrenocortical cells from Sceloporus lizards

Effects of adrenal corticosteroids on reproductive and endocrine functions of the gonads are well known, but reciprocal effects of gonadal hormones on the hypothalamo-pituitary-adrenal (HPA) axis and on adrenocortical steroidogenesis in particular have received much less attention. We investigated effects of gonadectomy and testosterone (T) replacement on adrenocortical cell function in a year-long field study of male Sceloporus undulatus (Eastern Fence Lizard) and in a shorter term laboratory study with male Sceloporus jarrovii (Yarrow's Spiny Lizard). We also compared females to males in Sceloporus virgatus (Striped Plateau Lizard) and investigated effects of gonadectomy in short-term laboratory experiment on females of this species. As measured by in vitro production of progesterone (P(4)), corticosterone (B), and aldosterone (ALDO), sensitivity of adrenocortical cells to corticotrophin (ACTH) was lower in control males than females of S. virgatus. In S. jarrovii males, cellular sensitivity to ACTH was reduced by orchiectomy but was not restored to levels of intact controls by T replacement. By contrast, in S. undulatus, cellular sensitivity to ACTH was not affected by orchiectomy alone but was reduced by T replacement in orchiectomized males. Maximal rates of steroid production were less consistently affected by experimental treatments, but were lower in males than in females of S. virgatus and were dramatically reduced by T replacement in orchiectomized S. undulatus males. Overall, our experiments clearly demonstrate two distinct sources of variation in functional capacities of dispersed adrenocortical cells isolated from Sceloporus lizards: (1) naturally occurring differences between males and females (Carsia and John-Alder, 2003), and (2) species-dependent changes in response to surgical gonadectomy with or without exogenous testosterone. Sex differences and functional lability in adrenocortical cells are probably widespread among vertebrates and may be an important component of variation in output of the HPA.

Structural model of an antistasin/notch-like fusion protein from the cocoon wall of the aquatic leech, Theromyzon tessulatum

The aquatic leech, Theromyzon tessulatum, secretes a proteinaceous cocoon with extraordinary physical properties (e.g., proteolytic, thermal resiliency). The deduced amino acid sequence of a major protein (Tcp-Theromyzon cocoon protein) from the T. tessulatum cocoon wall has been used to model the endogenous structure of the Tcp protein. The Tcp protein sequence comprises six internal repeats, each containing 12 ordered Cys residues. Amino acid alignments suggest that the region Cys1-->6 is homologous to antistasin, a leech anticoagulant, and Cys7-->12 is homologous to an epidermal growth factor-like domain found in notch-class proteins, which play critical roles in development, signaling, and adhesion throughout the Animalia. Modeling of individual domains (i.e., antistasin and notch) positions multiple hydrophobic and charged residues on the surface. When the antistasin and notch domains were fused, hydrophobic pockets appeared that may facilitate a polymerization mechanism. Collectively, the predicted features of our Tcp model are consistent with the physical properties of the leech cocoon wall.

A cysteine-rich protein in the Theromyzon (Annelida: Hirudinea) cocoon membrane

The aquatic leech, Theromyzon rude, secretes a flexible, proteinaceous cocoon that is resistant to a broad range of denaturing conditions (e.g. heat, denaturing chemicals). We have partially solubilized the Theromyzon cocoon membrane in 10% acetic acid and identified two major protein fragments. Microsequencing of both Theromyzon cocoon protein (Tcp) fragments generated an identical stretch of the amino-terminal sequence that was used to clone the corresponding gene. The predicted linear amino acid sequence of the resulting cDNA contained an unusually high cysteine content (17.8%). Sequence analysis identified six internal repeats, each comprising 12 ordered Cys residues in a approximately 62 amino acid repeating unit. Sequence comparisons identified homology with undescribed, Cys-rich repeats across animal phyla (i.e. Arthropod, Nematoda).

Influence of oxygenated fuel additives and their metabolites on gamma-aminobutyric acidA (GABAA) receptor function in rat brain synaptoneurosomes

Experimental and occupational inhalational exposure to oxygenate fuel additives in reformulated gasoline has been reported to induce neurological symptoms (e.g., headache, nausea, dizziness). We reported previously that the ether additives (methyl-t-butyl ether (MTBE), t-amyl-methyl ether (TAME) and ethyl-t-butyl ether (ETBE)) and their metabolites (t-amyl alcohol (TAA), t-butyl alcohol (TBA) and ethanol) alter the binding of [3H]t-butylbicycloorthobenzoate ([3H]TBOB), a ligand for the gamma-aminobutyric acidA (GABAA) receptor in rat brain membrane preparations. To more directly assess the effects of the ethers and their alcohol precursors on GABAA receptor function, the uptake of 36Cl- was measured in synaptoneurosomes, a preparation of closed membrane sacs comprised of pre- and postsynaptic membranes from adult rat cerebral cortex. Each of the compounds caused a concentration-dependent enhancement of muscimol-stimulated uptake of 36CI-, which diminished with further increasing concentrations. The potency of the enhancement by the compounds was in the rank order: MTBE = TAME > TAA = ETBE > TBA > ethanol. The half-maximally effective concentration (EC50) for the facilitation of muscimol-stimulated 36Cl- uptake ranged from 0.06 to 3 mM, and that for the higher-dose inhibitory effect (IC50) ranged from 3 to 50 mM. The facilitatory concentrations of the compounds are in the range of the blood concentrations reported in experimental animals after exposures known to induce CNS effects such as ataxia. The results suggest a potential role of the GABAA receptor in some of the reported neurotoxic effects of gasoline additives.

Outcome of primary vesicoureteric reflux detected following fetal renal pelvic dilatation

OBJECTIVE

Postnatal investigation of mild degrees of fetal hydronephrosis has allowed subsequent detection of infants with vesicoureteric reflux (VUR). This study was designed to provide short to medium term information on such infants who had primary VUR, the rates of renal damage and progression over time, the risk factors for such damage and to compare the characteristics of those who had mild dilatation of the fetal renal pelvis (4-9 mm) with those who had moderate-severe dilatation (> or = 10 mm).

METHODOLOGY

Since June 1989, infants whose antenatal sonography had identified a fetal renal pelvis with an anteroposterior diameter of > 4 mm were investigated postnatally with renal ultrasonography and micturating cystourethrogram (MCU), and placed on antimicrobial prophylaxis. Those with VUR received 99mTc-dimercaptosuccinic acid (DMSA) scintigraphy. Infants were followed until discharge based on resolution of VUR, surgery, or low grade VUR. A 5.5 year cohort between June 1989 and December 1994 formed the study population. A review of notes and clinical review (if still under follow up) was undertaken. Vesicoureteric reflux on MCU was regraded according to the International Classification, and reflux nephropathy on DMSA scans was regraded according to criteria proposed by Goldraich. Regression analysis was used to assess risk factors for renal damage.

RESULTS

There were 69 infants (37 girls, 32 boys) who were identified with primary VUR, with 37/69 having bilateral reflux. Eight had a urinary tract infection during the follow-up period. There was a broad distribution of grades of reflux detected (Grades I-3, Grades II-23, Grades III-19, Grades IV - 17, Grades V-7). 99m-Tc-dimercaptosuccinic acid scans on 57/69 (83%) demonstrated renal damage in eight infants (14%). This was predominantly global contraction of function. No progression of renal damage was seen over 2-7 years. Regression analysis showed a strong association between Grades IV, V reflux and the presence of renal damage (P < 0.001). Review of the degrees of fetal renal pelvic dilatation showed that 60/69 infants were detected because of mild (4-9 mm) dilatation. The majority (43/60) had lower grades of reflux (Grades I, II, 3), but there was no obvious cut-off between 4 and 9 mm that could predict high grade VUR (Grades IV, V).

CONCLUSIONS

The use of 4 mm to define an abnormal fetal renal pelvis allows a much larger group of infants with high grade primary VUR to be detected than if a higher cut-off measurement is used. Although it also detects many more infants with low grade primary VUR, there is no obvious cut-off point at which this effect predominates. Progressive renal damage was not seen in follow up of up to 7 years of age. Renal damage on DMSA scanning in this group is almost exclusively a pattern of global contraction of function. The presence of high-grade VUR appears to be the only important factor in predicting the presence of renal damage.

Dietary protein restriction stress in the domestic fowl (Gallus gallus domesticus) alters adrenocorticotropin-transmembranous signaling and corticosterone negative feedback in adrenal steroidogenic cells

Previous work with growing chickens (Gallus gallus domesticus) indicates that transient dietary protein restriction induces long-term enhancement of adrenal steroidogenic function in response to adrenocorticotropin (ACTH). The present study investigated two possible cellular functions mediating this enhanced response: (a) ACTH signal transduction and dissemination and (b) short-loop feedback inhibition of ACTH-induced corticosterone production by exogenous corticosterone. Cockerels (2 weeks old) were fed isocaloric synthetic diets containing either 20% (control) or 8% (restriction) soy protein for 4 weeks. Adrenal glands were processed for the isolation of adrenal steroidogenic cells nearly devoid of chromaffin cells ( approximately 90% adrenal steroidogenic cells). Results of experiments to assess signal transduction and dissemination indicated that protein restriction selectively enhanced ACTH-induced corticosterone production mediated by the cyclic AMP (cAMP)-dependent pathway. In addition, protein restriction substantially counteracted exogenous corticosterone-dependent inhibition of acute ACTH-induced corticosterone production (by 40.7% vs control). The proximal portion of the cAMP pathway seemed most affected by this stressor. Protein-restricted cells exhibited enhanced homologous sensitization to ACTH (136% greater than that of control cells) which appeared to be localized at a step(s) prior to or at the formation to cAMP. Also, maximal ACTH-induced cAMP production and sensitivity to ACTH in terms of cAMP production by protein-restricted cells were, respectively, 2.2 and 15.8 times those of control cells. However, variable results were obtained from other experiments designed to pinpoint the altered early steps in ACTH-transmembranous signaling. For example, with intact cells, cAMP responses to cholera toxin (CT) and forskolin (FSK) did not corroborate the results suggesting an augmentation of ACTH-signal transduction induced by protein restriction. Furthermore, basal and stimulatable (by ACTH, CT, FSK, and NaF) adenylyl cyclase activities from membranes from protein-restricted cells were, respectively, 47.2 and 40.2% less than those from control cells (normalized to 10(7) cell equivalents of crude membranes). Collectively, these findings suggest that protein restriction stress potentiates ACTH-induced corticosterone secretion by chicken adrenal steroidogenic cells in at least two ways: (1) on the proximal end, by modulating unknown factors which enhance cellular sensitivity to ACTH, ACTH receptor-adenylyl cyclase coupling, and adenylyl cyclase activity, and (2) on the distal end, by suppressing end-product corticosterone negative feedback, thus facilitating an increase in net corticosterone secretion.

Dietary protein restriction stress in the domestic turkey (Meleagris gallopavo) induces hypofunction and remodeling of adrenal steroidogenic tissue

In the present study, we investigated the influence of dietary protein restriction stress on adrenal steroidogenic function of the domestic turkey. Immature male turkeys (2 weeks old) were fed isocaloric synthetic diets containing either 28% (control) or 8% (restriction) soy protein for 4 weeks. Trunk plasma was processed for the determination of adrenocorticotropin (ACTH), corticosterone, aldosterone, and total 3, 5, 3'-triiodothyronine (T3). In addition, adrenal glands were processed for the isolation of defined, density-separable, adrenal steroidogenic cell subpopulations: three low-density adrenal steroidogenic cell subpopulations [LDAC-1 (rho = 1.0350-1.0490 g/ml). LDAC-2 (rho = 1.0490-1.0570 g/ml), and LDAC 3 (rho = 1.0370-1.0585 g/ml)] and a high-density subpopulation [HDAC (rho = 1.0590-1.0720 g/ml)], and the steroidogenic function of these cell subpopulations was evaluated. Protein restriction did not influence plasma ACTH However, it increased relative adrenal weight (mg/100 g body wt) (+37.8%) and plasma corticosterone (+317%). By contrast, it depressed plasma aldosterone (-51.2%). In addition, it caused a modest depression in plasma T3 (-25.9%). At the cellular level, protein restriction induced panhypofunction. Basal corticosteroid (aldosterone and corticosterone) production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds were, respectively, 42.9, 47.9, 30.8, and 57.5% less than those of corresponding cell subpopulations from control birds. In addition, maximal corticosteroid production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds, in response to ACTH, angiotensin II (AngII), and 25-hydroxycholesterol support, were depressed by 56.8, 55.1, 22.7, and 42.9%, respectively. Interestingly, LDAC-3 was relatively refractory to the influence of this stressor. By contrast, there was the lack of a concentration-dependent aldosterone response of LDAC-1 and -2 to AngII with protein restriction. This was not due to a failure in cell function since aldosterone responses of these cell subpopulations to ACTH and to 25-hydroxycholesterol support were apparent. In addition, the concentration of AngII receptors of cell subpopulations from protein-restricted turkeys, if anything, was greater than that of cell subpopulations from control turkeys. Protein restriction also altered the cell subpopulation composition of the adrenal gland: compared to control, it decreased the proportion of LDAC-2 by 42.3% and increased the proportion of LDAC-3 and HDAC by 68.7 and 302%, respectively. Thus, dietary protein restriction induces adrenal steroidogenic hypofunction in turkeys. In addition, the present study suggests that this nutritional stressor induces marked remodeling of the steroidogenic tissue in the turkey adrenal gland.

The effect of ethanol on muscarinic receptor-G protein coupling in the rat cortex

To understand the mechanism of ethanol action on G protein-mediated signal transduction pathway, the effect of ethanol on muscarinic receptor-G protein coupling in the rat cerebral cortex was examined. Acetylcholine (ACh)-stimulated G protein GTPase activity was used as an index of receptor-G protein coupling. ACh stimulation of G protein GTPase activity was time- and concentration-dependent, and atropine-sensitive. Rats injected with ethanol (3 g/kg body weight) were sacrificed after 4 hr, and the cerebral cortices removed. The ability of ACh to stimulate GTPase activity was similar in cortical cell membranes obtained from control and ethanol-treated rats; ACh maximally stimulated the enzymatic activity by 22% in membranes from both groups of rats. Next, in cortical cell membranes obtained from control rats (i.e., not injected with ethanol) the ability of ACh to stimulate GTPase activity in the presence of ethanol was examined. ACh stimulated GTPase activity in a concentration-dependent manner; the activity was 12.3 +/- 0.1, 14.5 +/- 0.64, 15.7 +/- 0.54, and 16.1 +/- 0.33 Pi pmol/min/mg protein, at 0, 0.01, 0.1, and 1 mM ACh, respectively (P < 0.05). In the presence of 100 mM ethanol ACh-stimulated GTPase activity was significantly inhibited. The IC50 value of ethanol inhibition of ACh-stimulated GTPase activity was approximately 50 mM. These results suggest that: 1) in vitro, ethanol impairs ACh-stimulated G protein GTPase activity in the rat cortical cell membranes, and 2) in vivo, the acute effects of alcohol on G protein function may be transient and reversible.

Drugs that influence tubulin polymerization modulate thyrotropin-releasing hormone receptor number in AtT-20 cells

In order to examine the role of cytoskeleton in modulating the cell surface receptors, AtT-20 cells (stably expressing thyrotropin-releasing hormone receptors) were incubated with drugs that are known to modify the tubulin-microtubule system. The binding of [3H]methyl thyrotropin-releasing hormone ([3H]mTRH) to intact cells increased as a function of time, and was linear from 1.25 x 10(6) to 6.25 x 10(6) cells/ml. Cells incubated with colchicine, vinblastine, and taxol for 16 hr were harvested and the cell concentration was determined using a haemocytometer. Because the drugs inhibited the cell proliferation at 100 nM, it was decided to examine the effect of 100 nM of each of the three drugs on the ability of [3H]mTRH to bind cell surface receptors. Cells were incubated with the drugs for 16 hr at 37 degrees. After the incubation, cells (5 x 10(6) cells/ml) from each group were assayed for [3H]mTRH binding. Colchicine, vinblastine, and taxol stimulated [3H]mTRH binding by up to 27, 27, and 21%, respectively, without altering the Ka of the ligand to the receptor. These results suggest that perturbation of cytosolic microtubules leads to a reorganization of the spatial location of hormone receptors.

Lead alters growth and reduces angiotensin II receptor density of rat aortic smooth muscle cells

Environmental lead (Pb2+) contributes a small but significant risk to human hypertension. It is postulated that the hypertensinogenic action of Pb2+ may be due, in part, to its direct action on vascular smooth muscle cells. To investigate this hypothesis, freshly isolated rat aortic smooth muscle (RASM) cells were propagated in defined media containing one of two Centers for Disease Control-based concentrations of Pb2+ (as lead citrate): 100 and 500 micrograms Pb2+/l (i.e., equivalent to 5.5 and 27.5 micrograms Pb2+/dl blood; designated 100-RASM and 500-RASM). Control (CON-RASM) cells received sodium citrate. 500-RASM cells exhibited suppressed propagation and fell out of propagation synchrony with CON-RASM cells: when CON-RASM cell approached confluence (approximately 90%), 500-RASM cell density was 6.4% that of CON-RASM cell density. By contrast, 100-RASM cells exhibited marked hyperplasia albeit this was not apparent until passage 3 (p3). Overall, when p3-p6 CON-RASM cells approached confluence, 100-RASM cell density was 107.6% greater than CON-RASM cell density. The protein content of CON-RASM and 100-RASM was not different, whereas that of 500-RASM cells was 29% greater than that of CON-RASM and 100-RASM cells. Phase-contrast microscopy revealed that 100 micrograms Pb2+/l converted normal spindle-shaped/ribbon-shaped RASM cells into less spread, cobblestone-shaped, neointimal-like cells. Immunocytochemical analysis revealed that 100-RASM cells lacked or had markedly fewer actin cables, characteristic of rapidly dividing cells. In addition, Pb(2+)-treated RASM cells exhibited altered membrane fatty acyl composition with a trend towards an increase (by as much as 50%) in membrane arachidonic acid. Interestingly, hyperplastic 100-RASM cells exhibited a 70.6% reduction in angiotensin II (Ang II) receptor concentration whereas the concentrations of alpha 1- and beta-adrenergic and atrial natriuretic peptide (ANP) receptors were not affected. In addition, in experiments designed to control for Pb(2+)-associated differences in RASM cell propagation, there was a concentration-dependent decrease in Ang II receptor concentration: for 100 and 500 micrograms Pb2+/l, Ang II receptor concentration was decreased 39.6% and 65.5%, respectively. Thus, although Pb2+, depending on its concentration, had contrasting effects on RASM cell propagation, it had a consistent, concentration-dependent inhibitory effect on Ang II receptor concentration. Recovery (r) from Pb2+ required at least two additional passages. At p71r the enhanced propagation (+54%) and reduced Ang II receptor concentration (-49%) of 100r-RASM cells persisted.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial natriuretic peptide stimulates aldosterone production by turkey (Meleagris gallopavo) adrenal steroidogenic cells

The inhibitory action of atrial natriuretic peptides (ANPs) on mammalian aldosterone synthesis is well documented. In addition, other work indicates that ANP and an analogue of its second messenger, 8-Br-cGMP, inhibit aldosterone production by chicken adrenal steroidogenic cells. However, the interaction between angiotensin II (AII) and ANP in the regulation of avian aldosterone production is poorly understood because chicken adrenal steroidogenic cells, the commonly used in vitro avian model, are comparatively unresponsive to AII. By contrast, turkey (Meleagris gallopavo) adrenal steroidogenic cells are sensitive to AII. Thus, in the present study, the action of ANPs and related peptides and their interaction with other stimulators of aldosterone production were investigated using freshly isolated and briefly cultured turkey adrenal steroidogenic cells. Surprisingly, several ANPs [rat (r), human (h), chicken (c)], and rat brain natriuretic peptide (rBNP) were as efficacious as [Ile5]AII for stimulating aldosterone production (2 hr) in freshly isolated cell suspensions but were less potent than [Ile5]AII (ED50 of ANPs approximately 5-10 nM; [Ile5]AII ED50 approximately 0.1 nM). In addition, chicken ANP enhanced maximal aldosterone production induced by [Ile5]AII (1 nM), K+ (25 mM), and hACTH-(1-39) (ACTH) (1 nM): maximal enhancement of the action of these secretagogues was +49%, +137% and +15%, respectively (P < 0.05; n = 3). Furthermore, other ANPs and related peptides [rBNP and bovine aldosterone secretion inhibiting factor (bASIF)] enhanced maximal [Ile5]AII-induced aldosterone production: the order of maximal enhancement was rBNP (+180%) > hANP/rANP (+50%) > bASIF (+25%) (P < 0.05; n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for functionally distinct subpopulations of steroidogenic cells in the domestic turkey (Meleagris gallopavo) adrenal gland

A body of histological and functional evidence supports the hypothesis that there are functionally distinct subpopulations of steroidogenic cells comprising the avian adrenal gland. In the present study, we tested this hypothesis by evaluating the steroidogenic responses of density-dependent subpopulations of adrenal steroidogenic cells isolated from domestic turkeys fed either a high-normal (control) sodium diet (0.4% Na+) or a Na(+)-restricted diet (0.04% Na+) for 8 days, the latter to stimulate the activity or appearance of possible zona glomerulosa-like cells. Subpopulations were visually yet reproducibly determined by their density-dependent separation on a continuous density gradient of Percoll (45%). The subpopulations were arbitrarily ascribed as being either low-density or high-density adrenal steroidogenic cells [LDAC (p = 1.0350-1.0585 g/ml) and HDAC (p = 1.0590-1.0720 g/ml), respectively]. LDAC and HDAC comprised 95.2 and 4.8%, respectively, of the total number of adrenal steroidogenic cells isolated. The LDAC was further subdivided into three visually distinct subpopulations. The functional differences between the LDAC subpopulations is discussed but was less dramatic than the functional distinction between the HDAC subpopulation and the pooled LDAC subpopulations. Basal aldosterone production values between control LDAC and HDAC were equivalent. In addition, there were no differences in maximal aldosterone production between control LDAC and HDAC in response to [Ile5]angiotensin II (AII), the avian equivalent, [Val5]AII, K+ (as KCl), and that supported by exogenous corticosterone. However, maximal aldosterone production in response to human ACTH-(1-39) (ACTH) of the LDAC was 32% greater than that of the HDAC. Na+ restriction enhanced basal aldosterone production of the LDAC by 84% over the control LDAC. In addition, it enhanced maximal aldosterone production of the LDAC in response to AII peptides, K+, ACTH and that supported by corticosterone by 54, 164, 83, and 74%, respectively, over that of the control LDAC. However, Na+ restriction disproportionately enhanced basal aldosterone production of the HDAC by 348% over that of the control HDAC. In addition, with Na+ restriction, maximal aldosterone production of the HDAC in response to AII, K+, and ACTH and that supported by exogenous corticosterone was consistently greater than that of the LDAC. Moreover, with Na+ restriction, maximal aldosterone production of the HDAC in response to AII peptides and K+ was increased over that of the control HDAC to a greater extent than was maximal aldosterone production in response to ACTH and that supported by corticosterone (% enhancement over control was as follows: AII peptides, 502%; K+, 668%; ACTH, 273%; corticosterone, 183%).(ABSTRACT TRUNCATED AT 400 WORDS)

Dissociation of increases in intracellular calcium and aldosterone production induced by angiotensin II (AII): evidence for regulation by distinct AII receptor subtypes or isomorphs

In mammalian zona glomerulosa cells, angiotensin II (AII)-induced increases in intracellular Ca2+ ([Ca2+]i) and AII-induced aldosterone production seem to be inextricably linked. However, in avian adrenal steroidogenic (adrenocortical) cells studied thus far, inducible aldosterone production seems to be insensitive to alterations in the mobilization of cellular Ca2+. This raises the hypothesis that alternative signal transduction pathways are implemented to induce aldosterone production in avian adrenocortical cells. In the present study, this hypothesis was investigated by using isolated turkey (Meleagris gallopavo) adrenocortical cells that are known to be three times more sensitive to AII than to ACTH for aldosterone production. In isolated turkey adrenocortical cells, the mammalian AII receptor antagonist, [Sar1,Ile8]AII, was as efficacious as [Ile5]AII in stimulating aldosterone production, albeit it had about 1/150 the potency of [Ile5]AII. The actions of both analogs required extracellular K+, suggesting a voltage-sensitive event. However, a maximal aldosteronogenic concentration of [Sar1,Ile8]AII not only failed to increase [Ca2+]i but also completely blocked maximal (10(-8) M)[Ile5]AII-induced increases in [Ca2+]i when added before [Ile5]AII and partially dampened (approximately 50%) maximal [Ile5]AII-induced increases in [Ca2+]i when added after (3 min) [Ile5]AII. This blockade in [Ca2+]i elevation was surmounted by high concentrations of [Ile5]AII (> 10(-6) M). By contrast, [Sar1,Ile8]AII did not alter maximal aldosterone production induced by [Ile5]AII and vice versa, thus suggesting that the action of both analogs converged on the same aldosteronogenic pathway, and that AII-induced aldosterone production was not coupled to elevations in [Ca2+]i. Detailed homologous-heterologous ligand-binding analyses supported the presence of two AII-binding sites that were discriminated by [Sar1,Ile8]AII (dissociation constants, 4.2 +/- 1.4 and 21.9 +/- 2.2 nM; concentration distribution, approximately 40% and approximately 60%, respectively; mean +/- SE, n = 4) but not by [Ile5]AII (dissociation constant, 2.1 +/- 0.1 nM for both sites). In addition, [Sar1,Ile8]AII- and [Ile5]AII-binding sites exhibited different physicochemical and pharmacological properties. The sensitivity of [Sar1,Ile8]AII-binding sites was about twice that of [Ile5]AII-binding sites to dithiothreitol. In addition, whereas both the high- and low-affinity sites detected by [Sar1,Ile8] AII exhibited equivalent competitive sensitivities to the type-1 receptor, the nonpeptidic antagonist, losartan (DuP 753), the sensitivity of the low-affinity site was 2.7 times that of the high-affinity site to the type-2 receptor, nonpeptidic antagonist, PD123319. Taken collectively, the data suggest that in turkey adrenocortical cells, elevations in [Ca2+]i and aldosterone production are dissociable events regulated by distinct AII receptor subtypes or isomorphs.

Properties of angiotensin II receptors of domestic turkey (Meleagris gallopavo) adrenal steroidogenic cells

In the present study, the properties of angiotensin II (AII) receptors of intact domestic turkey adrenal steroidogenic cells were characterized. AII (but not ACTH) induced an immediate and sustained increase in intracellular Ca2+. In addition, dithiothreitol inhibition of maximal AII-induced aldosterone production was closely correlated with its inhibition of binding suggesting that these receptors are type 1-like and operate through a non-"spare" receptor mode. Equilibrium-binding analysis revealed a single class of binding sites at a concentration of 63,500 sites/cell and having an apparent dissociation constant (Kd) of 1.21 nM. However, the Kd derived from kinetic analyses, 0.27 nM, was lower. Both empirically determined and model-based calculated distributions of bound hormone indicated that at equilibrium, about 30% of hormone-receptor complexes were internalized whereas 70% remained on the surface. This distribution contrasts sharply with that reported for mammalian (rat) adrenocortical cells. In keeping with recent cloning studies, these avian AII receptors of intact adrenal steroidogenic cells discriminated angiotensins and mammalian peptidic and nonpeptidic antagonists differently from mammalian adrenocortical and duck adrenal receptor preparations. Importantly, turkey adrenal steroidogenic cell AII receptors poorly discriminated the nonpeptide antagonists, losartan (DuP 753) (type-1 specific) and PD123177 (type-2 specific). Thus, AII receptors of freshly isolated, intact turkey adrenal steroidogenic cells are pharmacologically distinct from mammalian adrenocortical type-1 receptors.

Regulation of aldosteronogenesis in domestic turkey (Meleagris gallopavo) adrenal steroidogenic cells

The hormonal and cationic regulation of aldosterone production by freshly isolated turkey (Meleagris gallopavo) adrenal steroidogenic cells was investigated. Angiotensin II (AII), ACTH [human ACTH-(1-39)], and K+ stimulated aldosterone production in a concentration-dependent manner albeit these agents exhibited considerable differences in lag time for the significant stimulation of aldosterone production over basal production. By contrast, Ca2+ was without effect except at a high concentration (10 mM). Although ACTH was more efficacious than AII, it had about one-third the potency of AII for stimulating aldosterone production. However, ACTH potentiated the maximal aldosterone response to AII [maximal enhancement (+499%) at 3 x 10(-10) M ACTH]. Extracellular K+ was an absolute requirement for AII-induced aldosterone production (threshold concentration = 3 mM), and maximal enhancement (+200%) occurred with 5 mM (a physiological concentration). Although extracellular Ca2+ was not an absolute requirement for inducible aldosterone production, it enhanced AII-induced aldosterone production in a concentration-dependent manner [maximal enhancement (+727%) at 3 mM], albeit it did not alter the half-maximal steroidogenic concentration (EC50) of AII. Ca2+ also enhanced maximal ACTH-induced aldosterone production but to a lesser extent (+96% with 1 mM Ca2+). However, Ca2+ dramatically enhanced ACTH potency (ED50) (nearly 100 times at 1 mM Ca2+). The acute augmentation of AII-induced aldosterone production by ACTH, K+, and Ca2+ was not accompanied by increases in the cellular concentration and affinity of AII receptors, suggesting that the agents acted at intracellular loci distal to the AII receptor. Several aspects of the present study with isolated turkey adrenal steroidogenic cells differ markedly from those of studies with isolated chicken (Gallus gallus domesticus) adrenal steroidogenic cells and mammalian zona glomerulosa cells, thus suggesting interclass and intraclass differences in homeothermic vertebrate adrenal steroidogenic regulation.

Isolation of turkey adrenocortical cell angiotensin II (AII) receptor partial cDNA: evidence for a single-copy gene expressed predominantly in the adrenal gland

A turkey adrenocortical cell AII receptor cDNA fragment (714 bp) was isolated by RT-PCR using oligonucleotide primers based on rat aortic smooth muscle (RASM) and bovine adrenal type-1 (AT1) receptor cDNA coding sequences as primers. Sequence analysis indicated 73% nucleotide identity and 78% amino acid identity to the RASM AT1 receptor. Notable differences were 1) two additional Cys at positions 92 and 99 (first extracellular loop), 2) deletion of amino acid 168, formation of a triplet Asn sequence (Asn 186, 187, 188) and substitution of Arg192 with Pro (second extracellular loop) and 3) two additional potential protein kinase C phosphorylation sites, Thr221 and Thr233 (third intracellular loop). Southern blot analysis indicated that the receptor is a product of a single-copy gene. Northern blot analysis indicated at least three mRNA transcripts (7.5, 3.5 and 2.0 kb) expressed predominantly in the adrenal gland.

Differences in the characteristics and distribution of rat luteal receptors for native and deglycosylated human choriogonadotropin

Previous work has suggested that rat luteal cells have two populations of LH/hCG receptors that are located in different parts of the cell membrane. The possibility that these two receptor pools may have functional differences has been investigated through examination of the binding and action of native and deglycosylated hCG to different membrane fractions. Ovaries from eCG/hCG-primed immature female rats were separated into 1,000 x g (heavy) and 20,000 x g (light) particulate fractions. Increasing concentrations of NaCl had a biphasic effect on the binding of native and deglycosylated hCG to both membrane fractions, causing an increase in binding at low concentrations and a decrease in binding at higher concentrations. The binding of deglycosylated hCG to both membrane preparations and the binding of native hCG to light-membrane preparations was maximal at approximately the same NaCl concentration (50-65 mM). This was higher than the concentration of NaCl necessary for maximal binding of native hCG to the heavy-membrane preparation. In addition, maximal native hCG binding to this preparation occurred over a broader NaCl concentration range (15-65 mM). Equilibrium binding experiments showed differences in hCG binding to both fractions. In light membranes there were significantly more receptor sites for deglycosylated hCG (11.2 +/- 4.8 fmol/mg ovary) than for native hCG (4.8 +/- 0.7 fmol/mg ovary), with no significant different in affinity. In contrast, in heavy membranes the affinity for deglycosylated hCG (6.30 +/- 0.19.10(9) M-1), was significantly higher than that for native hCG (2.60 +/- 0.13.10(9) M-1), with no significant differences in receptor number.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of the lutropin/choriogonadotropin receptor in rat ovary during luteinization

Molecular analysis of the induction of the lutropin/choriogonadotropin receptor during the process of luteinization of the rat ovary was performed. The appearance of receptor binding activity and an immunological analysis of the receptor using Triton solubilized membrane proteins show little receptor present in luteal tissue through day 3 subsequent to hCG treatment, with some in day 4, and a marked increase by day 5. A similar pattern was found in the analysis of RNA hybridizing to several probes derived from the published cDNA sequence suggesting that receptor induction occurs primarily at the level of transcription.

Effects of cations on binding of human choriogonadotropin

The effect of various salts on the binding of human choriogonadotropin to rat luteal membranes has been examined. Increasing salt concentrations had biphasic effects, initially increasing binding, then decreasing it. With NaCl, these effects were on both the affinity and the number of receptor sites. The affinity increased with increasing NaCl concentrations, to a maximum at 40 mM, and then decreased. Above 40 mM NaCl, the number of binding sites increased. NaCl also altered the effects of Mg2+ and guanyl nucleotides. At low ionic strength, Mg2+ was necessary to observe binding. Guanine nucleotides modulated this binding by decreasing the affinity. At 40 mM NaCl, Mg2+ increased receptor number without altering affinity. Guanyl nucleotides modulated this binding by reducing the number of sites to that observed in the absence of Mg2+. At 150 mM NaCl, Mg2+ and guanine nucleotides had no effect. The results suggest the presence of two pools of human choriogonadotropin receptor in rat corpus luteum, one coupled to the guanine nucleotide regulatory protein (Ns) and being Mg2+ dependent and guanine nucleotide sensitive, and the other not coupled to Ns and being Mg2+ independent and guanine nucleotide insensitive.

Hormonal modulation of guanyl nucleotide binding to rat luteal membranes

Guanyl nucleotides are known to play a dual role in the activation of the adenylate cyclase system of the rat corpus luteum, being required for human choriogonadotropin (hCG) stimulation of the enzyme and modulating hCG binding to some hormone receptors. Current models of adenylate cyclase activation require that guanyl nucleotide binding be enhanced by hormones, and we have examined this binding in rat luteal membrane preparations known to contain guanyl nucleotide-modulated hCG receptors. [3H] Guanylyl-imidodiphosphate (GMPPnP), a nonhydrolyzable analog of guanosine triphosphate (GTP), was used to investigate binding to urea-washed, heavy rat luteal membranes. Binding was found to be linear, with respect to the amount of membranes added, in the range of 2-10 mg wet wt. tissue equivalents, and equilibrium was reached after a 30-min incubation at 30 degrees C. Analysis of equilibrium binding experiments gave a Ka of 1.2.10(7) +/- 0.9.10(7) M-1, with 460 +/- 430 fmol binding sites per mg tissue in the absence of hormone, Kinetic experiments showed an association rate constant of 2.6.10(5) +/- 0.5.10(5) M-1 min-1 and a dissociation rate constant of 1.8.10(-2) +/- 0.9.10(-2) min-1. In the presence of hCG, the Ka was unchanged; however, the number of binding sites increased by 50-120%. Competitive binding assays utilizing other nucleotides revealed that a hierarchy of GMPPnP = GTP greater than guanosine diphosphate (GDP) greater than inosine triphosphate (ITP) in displacing labeled GMPPnP. A similar hierarchy was also found for hCG-stimulated adenylate cyclase activity (GMPPnP = GTP greater than ITP) and for modulation of hCG binding (GMPPnP greater than GTP greater than ITP).(ABSTRACT TRUNCATED AT 250 WORDS)

Exact orthogonal kernel estimation from finite data records: extending Wiener's identification of nonlinear systems

A technique is described for exact estimation of kernels in functional expansions for nonlinear systems. The technique operates by orthogonalizing over the data record and in so doing permits a wide variety of input excitation. In particular, the excitation is not limited to inputs that are white, Gaussian, or lengthy. Diagonal kernel values can be estimated, without modification, as accurately as off-diagonal values. Simulations are provided to demonstrate that the technique is more accurate than the Lee-Schetzen method with a white Gaussian input of limited duration, retaining its superiority when the system output is corrupted by noise.

Guanyl nucleotide regulation of human chorionic gonadotropin binding to rat luteal tissue

Guanyl nucleotides are known to have a dual effect on most hormone-sensitive adenylate cyclase systems, regulating activation of the adenylate cyclase enzyme and binding of hormone to receptor. In the ovary, guanyl nucleotides have been shown to be required for hCG stimulation of luteal adenylate cyclase, but no effect on binding has been observed. Evidence has been obtained which suggests that guanyl nucleotide regulation of hCG binding is masked in most luteal membrane preparations by the presence of a large excess of unregulated receptor. A highly purified urea-washed membrane fraction has been prepared. Binding of hCG to this preparation was decreased (approximately 45%) in the presence of 5'-guanylylimidodiphosphate (GMPPnP). The maximal effect of GMPPnP occurred at 10 microM, with the half-maximal effect at 0.2 microM. These levels compare favorably with the GTP concentrations required for hCG stimulation of luteal adenylate cyclase. Analysis of equilibrium binding experiments showed that GMPPnP acted by reducing the number of binding sites by 45%. However, kinetic experiments suggested that this effect was due to a significant decrease in the affinity of a fraction of the hCG-binding sites. Association of hCG and its receptor was unaffected by the presence of GMPPnP (100 microM), whereas the dissociation of 40-50% of bound hormone was significantly accelerated (30-fold) by its presence. The guanyl nucleotide effect required the presence of MG+2; other divalent cations (Ca+2, Mn+2, and Co+2 could not be substituted. The ratio of beta-adrenergic to hCG-binding sites in the urea-washed heavy membrane preparation was elevated, suggesting that a sizable fraction of uncoupled hCG receptor had been removed. The results show that hCG binding to its luteal receptor is modulated by guanyl nucleotide and suggest that the modulation only occurs in those receptors that are directly coupled to the adenylate cyclase enzyme.

Studies concerning a GTP regulatory subunit of rat luteal adenylate cyclase

The ADP-ribosylation of rat luteal membrane proteins has been investigated. In the presence of cholera toxin two membrane proteins, Mr 115,000 and 46,000, incorporated [32P]ADP-ribose from [32P]NAD+. The larger protein also incorporated [32P]ADP-ribose in the absence of cholera toxin. The smaller protein was identified as the guanine nucleotide regulatory protein of adenylate cyclase. To facilitate studies concerning this species, a simple and convenient method of measuring ADP-ribose incorporation into the protein was developed. Levels of the protein were found to be approximately equal to those of the hCG receptor and 7- to 10-fold higher than those of the beta-adrenergic receptor. Luteinization of rat ovaries by injection of hCG indicated that G/F concentrations increased approximately 2-fold over a 5- to 11-day period, and correlated significantly with increased beta-adrenergic receptors, and beta-adrenergic and NaF-stimulated adenylate cyclase, but not with hCG receptors or hCG-stimulated adenylate cyclase. The distribution of the G/F protein in purified luteal membrane preparations mimicked the distribution of adenylate cyclase activity. No evidence could be found for hormonally induced alterations in ADP-ribose incorporation into this protein under either ribosylation or adenylate cyclase conditions. The exact role of the protein in the activation of rat luteal adenylate cyclase has yet to be determined.

Effects of dansyl-arginyl-(4'-ethyl)piperidine amide on gonadotropin binding to rat tissues

The effects of dansyl-arginyl-(4'-ethyl)-piperidine amide (DAPA) on the binding of gonadotropins has been investigated. The compound inhibited the binding of hCG, human LH, and porcine LH to rat luteal membranes with an ED50 of 70 microM and the binding of human FSH to rat testicular membranes with an ED50 of 350 microM. Alteration of the substitution at the 4 carbon of the piperidine moiety altered the effect for hCG binding to luteal tissue, the ED50 being lowered with increased chain length (ED50 for H greater than methyl greater than ethyl greater than propyl = isobutyl) and shifted approximately half an order of magnitude for each carbon added. Analysis of equilibrium binding data for hCG to rat luteal membranes showed a decrease in the Ka with increasing DAPA concentrations (2.2 X 10(10), 1.0 X 10(10), and 0.4 X 10(10) M-1 for 0, 50, and 150 microM DAPA, respectively), with little or no effect on the number of sites. At a concentration of 50 microM, the compound did not affect the initial rate of association of the hormone and its receptor, but did change the dissociative behavior. After a short period of association, dissociation was followed in the absence and presence of DAPA. In all cases a biphasic dissociation was observed. The presence of DAPA slowed the rate constant for the fast phase (DAPA-treated, 4.7 X 10(-3) min-1; control, 7.6 X 10(-3) min-1) and reduced the fraction of total hCG undergoing the slow phase of dissociation (DAPA-treated, 60.6%; control, 77.4%). After a long period of association, the dissociation of hCG was monophasic, and the presence of DAPA increased the rate constant from 2.0 X 10(-4) to 4.4 X 10(-4) min-1. The results show that DAPA acted as an inhibitor of gonadotropin binding. The kinetic data suggest a sequential model of hormone binding in which the compound affected a step subsequent to the initial interaction.

Synergistic effects of chymotrypsin and human chorionic gonadotrophin on rat luteal adenylate cyclase

The effects of chymotrypsin on rat luteal adenylate cyclase have been investigated. Maximal stimulation occurred at a concentration of 10 micrograms/ml. This dose of chymotrypsin stimulated basal, GTP-,5'-(beta, gamma-imido)triphosphate-, and NaF-stimulated adenylate cyclase activity 2- to 3-fold. hCG-stimulated activities were stimulated 5- to 6-fold by the proteinase and showed a synergistic effect. The proteinase did not alter the hCG response curve, and the effect could not be mimicked by trypsin. Proteolytic activity was required, since chymotrypsinogen and inactivated chymotrypsin were not effective. The presence of chymotrypsin could not restore the hormonal sensitivity of a proteinase inhibitor-inactivated system. The results suggest that chymotrypsin stimulated rat luteal adenylate cyclase activity by two or more mechanisms: 1) a direct action on the catalytic subunit or a closely associated protein, and 2) an action somewhere in the pathway of hormonal stimulation.

Effects of proteinase inhibitors on adenylate cyclase

The effects of a number of proteinase inhibitors on rat ovarian and rat hepatic adenylate cyclase preparations were examined. N alpha-tosylarginine methyl ester, 7-amino-1-chloro-3-L-tosylamidoheptan-2-one, 1-chloro-4-phenyl-3-L-tosylamidobutan-2-one, 1-chloro-4-methyl-3-L-tosylamidopentan-2-one and other low-molecular-weight proteinase inhibitors blocked hormonally stimulated adenylate cyclase from either source with hepatic preparations requiring higher concentrations. Addition of nucleotides (ATP, GTP, GDP, CTP or ITP) to inhibited ovarian preparations did not reverse inhibition, nor did dithiothreitol reverse phenylmethanesulphonyl fluoride-inhibited ovarian adenylate cyclase. The kinetics of the inhibition of rat ovarian adenylate cyclase were examined by following the production of cyclic AMP after the addition of inhibitors to membrane preparations preincubated under assay conditions with human choriogonadotropin, guanosine 5'-[beta gamma-imido]triphosphate of NaF. 7-Amino-1-chloro-3-L-tosylamidoheptan-2-one, 1-chloro-4-phenyl-3-L-tosylamidobutan-2-one and 1-chloro-4-methyl-3-L-tosylamidopentan-2-one had two effects on human-choriogonadotropin-stimulated adenylate cyclase. At low concentrations (less than or equal to 0.2 mM) there was an irreversible inhibition of hormonally-stimulated cyclase with maximum first-order inhibitory rate constants of 0.05--0.08 min-1. At higher concentrations the irreversible effect persisted, but, in addition, there was a marked decrease in the cyclase initial velocity to 25--50% of that of control values. N alpha-tosylarginine methyl ester had similar effects; at low concentrations (less than or equal to 2 mM) it inhibited irreversibly, and at higher concentrations it decreased the initial velocity (50% at 10 mM). At high concentrations (greater than 3 mM) N alpha-tosylarginine methyl ester also inhibited NaF- and guanosine 5'-[beta gamma-imidol]-triphosphate-stimulated cyclase but in a reversible manner. 7-Amino-1-chloro-3-L-tosylamidoheptan-2-one inhibited NaF-stimulated adenylate cyclase in two ways, as for human-choriogonadotropin-stimulated adenylate cyclase, but required 10--20-fold higher concentrations. The low-concentration irreversible effect can be explained by a continual inactive in equilibrium active conversion of adenylate cyclase during hormonal stimulation in which the inactive to active conversion is blocked by the inhibitors. The high-concentration effect is a direct one on the active catalytic moiety of the enzyme.