Seasonal ultrastructural changes of the hypophyseal pars tuberalis in the hedgehog (Erinaceus europaeus L.)

The comparison of the hypophyseal pars tuberalis in active and in hibernating hedgehogs reveals different cytological characteristics in the specific secretory cells. In active animals, these cells show oval nuclei and the cytoplasm contains numerous secretory granules near or attached to the cell membrane, suggesting exocytotic release. In hibernating animals, the specific secretory cells are characterized by irregularly shaped and often invaginated nuclei. Clusters of secretory granules lying within the cytoplasm are often joined by lysosomes. These areas are observed to be encircled by cisterns of the endoplasmic reticulum. Degenerative processes in the structures sequestered in this way are interpreted as signs of crinophagy which has no equivalent in the cell types of the pars distalis.

Growth hormone releasing factor evokes rhythmic hyperpolarizing currents in rat anterior pituitary cells

1. The effect of human pancreatic growth hormone releasing factor (hpGHRF) on the electrical activity of dissociated rat anterior pituitary cells in culture was studied, using both the cell-attached and whole-cell modes of the patch-clamp recording technique. 2. To avoid possible wash-out of the responses, extracellular records were made from cell-attached patches. Application of hpGHRF to the cells produced rhythmic inward currents through the patches, attributable to rhythmic hyperpolarizations of the cell membrane outside the patch. The amplitude of the current oscillations was 1-8 pA and the frequency 0.05-0.4 Hz. 3. Flooding the cells with K+ ions from a small pipette containing 50 mM or 100 mM-K+ resulted in a reversible attenuation or block of the rhythmic inward currents evoked by hpGHRF, indicating that changes in K+ conductance were involved in the responses. 4. Flooding the cells with a solution containing 10 mM-EGTA blocked these rhythmic inward currents reversibly, suggesting the involvement of Ca2+ in the responses. In addition, responses were blocked by adding Co2+ (5-10 mM) to the bathing medium. The presence of tetrodotoxin (3 microM) had no effect, ruling out the participation of voltage-gated Na+ channels. 5. With whole-cell recording, the resting potential (-41.46 +/- 7.78 mV) and input resistance (5.34 +/- 3.73 G omega) of anterior pituitary cells in culture were found to be similar to those previously reported for pituitary cells and chromaffin cells with the same recording method. 6. In whole-cell experiments, application of hpGHRF (shortly prior to intracellular penetration) evoked rhythmic outward currents, associated with conductance increases, when the cells were clamped at their resting potential. The persistence of these currents in the 'voltage-clamped' cell indicated that the rhythmicity was not related to voltage-dependent phenomena. The currents disappeared within 4 min after breaking into the cell, presumably because of 'washout' of cell constituents into the pipette. 7. The reversal potential (-60 mV) of the hpGHRF-induced currents was negative to the resting potential of the cells (-41 mV), further indicating that hpGHRF would evoke rhythmic hyperpolarizations in unclamped cells, possibly due to periodic increases in K+ conductance. 8. The possible relation of these rhythmic currents to hpGHRF-induced secretion of growth hormone is discussed.

Influences of photoperiod on nuclear androgen receptor occupancy in neuroendocrine tissues of the golden hamster

Day length regulates the negative feedback potency of gonadal steroids upon luteinizing hormone (LH) in seasonal breeders such as the golden hamster. We have used an exchange assay employing 3H-R1881 to determine whether nuclear androgen plus receptor levels in the preoptic area, medial basal hypothalamus, or anterior pituitary differ between male hamsters maintained in long or short days. Cell nuclear androgen plus receptor levels in brain and anterior pituitary were significantly lower in intact males maintained in short days; these differences reflected significant decreases in testis size and serum testosterone (T levels upon exposure to inhibitory photoperiods. In castrated males in which serum T levels were 'clamped' by the insertion of T-filled Silastic capsules, exposure to short days was not correlated with an increase in preoptic area, medial basal hypothalamus, or anterior pituitary receptor occupancy even though T's negative feedback actions upon LH were clearly enhanced. In contrast, there were instances in which androgen receptor occupation was elevated in males exposed to long days. Our results suggest that in the male golden hamster, the well-documented increase in the ability of T to suppress LH secretion in short photoperiods cannot be attributed to an increase in receptor-mediated uptake and nuclear accumulation of androgen in target cells in the brain and anterior pituitary gland.

Adipose tissue, longissimus muscle and anterior pituitary growth and function in clenbuterol-fed heifers

The present study was conducted to determine the effects of feeding clenbuterol on adipose tissue and longissimus muscle growth in heifers. For 50 d, 14 heifers were fed either a sucrose-based, clenbuterol supplement or a placebo in which the clenbuterol had been omitted. The heifers were slaughtered in two groups, based on initial weight. Adipose tissue from several anatomical sites and longissimus muscle (depending on slaughter group) were obtained fresh at slaughter. Changes in carcass characteristics elicited by clenbuterol were similar to those reported by others for steers and sheep. Subcutaneous (sc) and intramuscular (im), but not perirenal, adipocytes were smaller and there were more cells per g tissue in the adipose tissue depots of the clenbuterol-fed heifers. Clenbuterol decreased lipogenic enzyme activities, fatty acid-binding protein activity, basal lipolysis and acetate incorporation into glyceride-fatty acids (P less than .05) in sc adipose tissue, but had no effect (P greater than .05) on lipogenesis or lipolysis in im adipose tissue. Clenbuterol elicited a 20% increase in type II myofiber diameters (P less than .05) but had no effect on type I myofiber diameters. In vitro growth hormone release by perifused anterior pituitaries was not affected significantly by long-term in vivo exposure to clenbuterol. These data indicate that a depression in lipogenesis is the mechanism by which clenbuterol decreases subcutaneous fat accretion in cattle.

[The use of a radioimmunologic method of analysis of 11-deoxycortisol for the evaluation of the function of the pituitary-adrenal cortex system during the metopirone test]

A radioimmunoassay of II-deoxycortisol in human and animal blood plasma was developed. The antiserum used in the method was prepared against a conjugate of II-deoxycortisol-3(0-carboxymethyloxime) and bovine serum albumin. Specificity of the antiserum was determined in cross reactions using 32 steroids. High specificity of the antiserum allowed to determine II-deoxycortisol without preliminary chromatographic isolation. Sensitivity of the method enabled to detect 25 pg of II-deoxycortisol. The intra- and interassay variations were less than 10% and 15%, respectively. The method was used for evaluation of hypophysis-adrenal cortex system functions under the conditions of metopirone test.

Photoperiodic sensitivity of prepubertal female Fisher 344 rats

The laboratory rat is thought to be a poor model for study of the photoperiodic control of reproduction; however, this has only been investigated in a few rat strains. The purpose of the present investigation was to determine if the neuroendocrine-reproductive system of the Fisher 344 (F344) rat, an inbred strain, is sensitive to light deprivation. All treatments were performed on 28-day-old female F344 rats and the animals maintained for 8 weeks in a 14:10 light:dark cycle. Blinding resulted in a 65% (P less than 0.01) reduction in uterine weight and a 25% (P less than 0.01) decrease in ovarian weight. Accompanying these reductions in blinded animals were significant inhibitions of anterior pituitary weight, serum prolactin levels, and pituitary prolactin synthesis as measured in vitro. Pinealectomy of the blinded animals prevented all of these effects. Additionally, when olfactory bulbectomy, a procedure known to sensitize rats to the effects of photoperiod, was combined with blinding, the results did not differ significantly from that found with blinding alone. From these data we conclude that 1) the neuroendocrine-reproductive system of the prepubertal F344 female rat is highly sensitive to light deprivation; 2) light deprivation produces its antigonadotrophic effect through the pineal gland; and 3) olfactory bulbectomy does not potentiate the effects of blinding in the F344 rat.

Pituitary hormones and aging

This article reviews the reported effects of aging on pituitary structure and function in man.

Coupling of inositol phospholipid hydrolysis to peptide hormone receptors expressed from adrenal and pituitary mRNA in Xenopus laevis oocytes

The expression of several neurotransmitter and drug receptors from injected exogenous mRNA in Xenopus laevis oocytes has been demonstrated by electrophysiological measurements of ion channel activation. The expression of specific receptors for peptide hormones in such a translation system would facilitate studies on the structure and regulation of cell-surface receptors as well as their coupling to membrane transduction mechanisms. The expression of receptors for calcium-mobilizing hormones in Xenopus oocytes was sought by analysis of phospholipid turnover in hormone-stimulated oocytes. For this purpose, Xenopus oocytes were injected with mRNA extracted from bovine adrenal and pituitary glands and incubated with myo-[3H]inositol to label plasma-membrane phosphatidylinositol phosphates. The expression of functionally active receptors for angiotensin II (AII) and thyrotropin-releasing hormone (TRH) was demonstrated by the stimulation of [3H]inositol phosphate production by AII and TRH in the mRNA-injected, [3H]inositol-prelabeled oocytes. The ability of AII and TRH to act by way of newly synthesized receptors from mammalian endocrine tissues to stimulate phosphatidylinositol polyphosphate hydrolysis in Xenopus oocytes suggests a generalized and conserved mechanism of receptor coupling to the transduction mechanism responsible for activation of phospholipase C in the plasma membrane.

Receptors mediating the CRH effects of vasopressin and oxytocin

The data highlighted here suggest that the CRH effects of vasopressin and oxytocin are mediated by one and the same hypophysial receptor which has unique pharmacological specificity. The nomenclature for this receptor type is not established; both V3(53) and V1 beta 39 have been proposed. The former proposal is logical if the pharmacology of ligand recognition is emphasized, whereas the latter designation takes into account that transmembrane signalling from V1 receptors occurs via coupling proteins Go and Gi but not Gs. Such issues are best resolved after cDNA cloning of the genes for the receptors: in the meanwhile the working definition V3 seems more convenient. Several studies show that pituitary V3 receptors are regulated by the concentration of vasopressin in hypophysial portal blood and the amount of glucocorticoid hormones in the circulation (see Ref. 9 for review). Work in this area should clarify further the intracellular mechanism of the CRH action of vasopressin, as well as the factors that determine the responsiveness of corticotrophs to various secretagogues. Most recently, it has been shown that vasopressin is a potent thyrotropin-releasing hormone. This finding extends further the growing concept that there is considerable "cross-talk" between the classical neuroendocrine axes. These were previously thought to be separated by the hypothalamic organization of "final common pathways" of neuroendocrine motoneurons in the hypothalamus, each producing a unique neurohormone to regulate a single type of adenohypophysial cell. It seems that the days of the validity of this hypothesis are numbered, and an important task will be to determine the possible physiological significance of the "cross-talk" within the hypothalamo-pituitary unit in the regulation adrenocortical function.

Receptors and secretory actions of sigma/phencyclidine agonists in anterior pituitary cells

Opiate receptor subtypes in the adenohypophysis were analyzed by binding studies with tritiated etorphine, phencyclidine (PCP), and N-allylnormetazocine [(+)SKF 10,047] in anterior pituitary cell (AC) cultures and membranes, and in cell populations separated by centrifugal elutriation. In cultured AC, specific binding of [3H]etorphine revealed two sets of saturable sites with Kd values of 5 nM and about 10 microM. The high affinity [3H]etorphine sites were present in low concentration and represent specific opiate receptors that mediate the direct inhibitory actions of etorphine and morphine on LH release in vitro. The more abundant low affinity sites, observed in the presence of higher concentrations of unlabeled opiates, exhibited the properties of sigma/PCP receptors. In intact AC and pituitary membranes, specific [3H]PCP binding was saturable with respect to labeled and unlabeled ligand concentrations, and Scatchard analysis revealed a single class of relatively high affinity [3H]PCP-binding sites (Kd = 98 nM in pituitary membranes). Relative potencies derived from inhibition of [3H]PCP binding in AC by PCP-related drugs were: (-) cyclazocine greater than dexoxadrol greater than N-[1-(2-Thienyl)cyclohexil]piperidine greater than PCP greater than (+)SKF 10,047 greater than levaxodral greater than (+)cyclazocine less than (-)SKF 10,047 greater than (+)ethylketocyclazocine greater than haloperidol greater than (-)ethylketocyclazocine. In elutriated pituitary cells, specific [3H]PCP binding was correlated with the LH content of the individual cell fractions. The binding of (+)-[3H]SKF 10,047 was also specific and saturable in AC and anterior pituitary membranes, which contained two classes of binding sites with Kd values of 87 nM and 3.3 microM. In fractionated pituitary cells, specific binding of (+)-[3H]SKF 10,047 was similar in enriched lactotrophs and gonadotrophs. The high affinity class of (+)-[3H]SKF 10,047-binding sites probably corresponds to sigma-receptors, and the low affinity class to PCP receptors. In contrast to the inhibitory actions of opiates on LH release in vitro, PCP and (+)SKF 10,047 stimulated LH release in cultured AC and enhanced the secretory responses to GnRH as well as KCl. The stimulation of LH release by PCP was dependent on extracellular calcium and is probably related to increased transmembrane calcium influx. The stimulatory sites may correspond to selective sigma/PCP receptors, and could represent a distinct nonopiate receptor subtype with the potential for modulation of gonadotropin secretion.

Inositol 1,4,5-trisphosphate binds to a specific receptor and releases microsomal calcium in the anterior pituitary gland

The properties of inositol 1,4,5-trisphosphate (InsP3) receptor sites in the anterior pituitary were evaluated by binding studies with InsP3 labeled with 32P to high specific radioactivity. Specific binding of Ins[32P]P3 was demonstrable in pituitary membrane preparations and was linearly proportional to the amount of membrane added over the range 0.5-2 mg of protein. Kinetic studies showed that specific InsP3 binding was half-maximal in about 40 sec and reached a plateau after 15 min at 0 degree C. Addition of 1 microM unlabeled InsP3 was followed by rapid dissociation of the bound ligand, according to a single exponential function with half-time of about 1 min. Scatchard analysis of the binding data was consistent with a single set of high-affinity sites with Kd of 1.1 +/- 0.4 nM and maximal binding capacity of 28 +/- 15 fmol/mg of protein (n = 6). The specificity of Ins[32P]P3 binding to these sites was illustrated by the much weaker affinity for structural analogs such as inositol 1-phosphate, phytic acid, 2,3-bisphosphoglycerate, and fructose 1,6-bisphosphate. To assess the functional relevance of the InsP3 binding sites, the Ca2+-releasing activity of InsP3 was measured in pituitary membrane preparations. In the presence of oligomycin (2.5 micrograms/ml), Ca2+ movements were monitored with the fluorescent indicator fura-2 (free acid). Under these conditions, 1 mM ATP caused rapid uptake of Ca2+ by a vesicular component of the membrane fraction. Addition of InsP3 (50-2000 nM) caused a dose-dependent release of Ca2+ with a half-maximal effect at 240 nM. In the presence of 3% polyethylene glycol, GTP also stimulated calcium release. However, a nonhydrolyzable GTP analog, guanosine 5'-[gamma-thio]triphosphate, did not release calcium and completely blocked the effect of GTP. Under physiological conditions within the cytosol, the high-affinity InsP3 binding sites characterized in pituitary membranes could serve as the putative receptors through which InsP3 triggers Ca2+ mobilization in the anterior pituitary gland.

Human relaxin increases cyclic AMP levels in cultured anterior pituitary cells

Although relaxin acts at several abdominal sites and mammary tissue associated with pregnancy and parturition, the scope of target tissues and the signals conveying the relaxin message into the cell are poorly defined. We found that human relaxin rapidly elevates the cyclic AMP content of cultured rat anterior pituitary cells. This is a graded response (EC50 0.3 nM relaxin) that can be blocked by anti-relaxin antibodies or the hormones somatostatin and dopamine. Furthermore, other hormones with some sequence homology to relaxin, such as insulin and insulin-like growth factor-I, have no such action. We conclude that the anterior pituitary may be a target tissue for relaxin and that cyclic AMP may act as an intracellular messenger for relaxin in these cells.

Gamma-aminobutyric acid modulates chloride channel activity in cultured primary bovine lactotrophs

The effects of GABA, the analogues muscimol and baclofen, and the antagonist bicuculline were investigated on cultured primary bovine lactotrophs using the patch clamp technique. Under voltage clamp in the whole cell mode using solutions containing chloride as the only permeable ion, GABA application increased the amplitude of mean membrane current and fluctuations of current about this mean. Statistical analysis of current fluctuations induced by GABA showed that the power density spectra in 8 of 12 cells were best fitted to double Lorentzian functions and the variance was smallest around the estimated equilibrium potential of chloride ions. The underlying channel open time estimated from noise analysis was only weakly voltage-dependent. The variance of current noise increased with GABA concentration within the range of 1-30 microM, although a slight decrease of variance in one cell could be observed at 30 microM, suggesting that desensitization to GABA might occur. Muscimol mimicked the effect of GABA but baclofen was without effect under these conditions. Bicuculline reduced the GABA-activated membrane current fluctuations. GABA- or muscimol-activated channels recorded in isolated outside-out patches had a slope conductance of about 20 pS. Mean open times of the channel were characterized by two exponential decay functions. We conclude that bovine lactotrophs have GABA-activated chloride channels, which appear to be voltage-independent. In addition, the action of GABA appears to be mediated through the GABAA receptor subtype.

Characteristics of phorbol ester stimulated growth hormone release: inhibition by insulin-like growth factor I, somatostatin, and low calcium medium and comparison with growth hormone releasing factor

TPA (12-O-tetradecanoylphorbol 13-acetate) is one of a class of compounds known as tumor promoters which perturb the inositol phosphate pathway in a number of cells. We have used TPA in a dispersed rat adenohypophysial cell system to probe the characteristics of growth hormone (GH) release. In this system we have found that the cells release GH in response to low concentrations of TPA: the EC50 was 0.23 +/- 0.05 nM (n = 6) and the maximal concentration was 5 nM. However, the maximal TPA-induced GH release was only 34 +/- 5% (n = 7) of the GH released by maximal growth hormone releasing factor (GRF) suggesting TPA releases a subpool of stored GH. Both somatostatin and insulin-like growth factor I inhibit GH release stimulated by TPA to the same extent as that stimulated by GRF, showing that the normal inhibitory control mechanism of release is not altered. Incubation in a low calcium medium that totally blocks GRF-stimulated GH release also inhibits TPA-stimulated GH release. The calcium channel blockers nifedipine and diltiazem both partly inhibit GRF- and TPA-stimulated GH release, showing some component of the calcium necessary for GH release arises from influx across the cell membrane.

Sodium and potassium currents involved in action potential propagation in normal bovine lactotrophs

1. The properties of whole-cell and single-channel Na+ and K+ currents in immunocytochemically identified bovine lactotrophs were studied using the patch-clamp technique. 2. In the whole-cell, current-clamp mode, cells had membrane potentials of -94.7 +/- 6.7 mV and input resistances of 2-17 G omega. Current-induced action potentials were recorded with a threshold around -35 mV and amplitude of 40-65 mV. Repetitive firing was not sustained at frequencies greater than 1-2 Hz without total inactivation. 3. Under voltage clamp, action potentials were shown to be composed of an inward TTX-sensitive Na+ current and an outward K+ current that was abolished by internal Cs+. 4. The isolated Na+ current had a threshold for activation around -35 mV and rapidly inactivated to a steady state during a test voltage pulse. Inactivation was strongly voltage-dependent, with the Na+ current being half-inactivated at -20 mV. 5. Recovery from inactivation was voltage dependent and at a holding potential of -60 mV, 50% reactivation was achieved after 420 ms. The implications of this long reactivation time on sustained action potential frequency are discussed. 6. Single Na+ channel activity was examined with the outside-out patch configuration and yielded single-channel conductances of 22.5 pS. Reconstruction of the voltage and time dependence of single-channel currents provided an accurate picture of the whole-cell Na+ current. 7. Whole-cell outward current carried by K+ in the absence of Na+ and Ca2+ had a large conductance, was slowly activated and demonstrated no inactivation. A second, more rapidly activating Ca2+-dependent K+ current could also be demonstrated. 8. Ensemble analysis of whole-cell K+ currents in the absence of Ca2+ showed underlying single-channel amplitudes of 1.2 pA at +10 mV, with the lactotroph having about 350 active channels at this potential. 9. Recordings of single K+ channels also demonstrated two classes of channel: a small (50 pS) voltage-activated channel and a higher-conductance (100 pS) Ca2+- sensitive channel. 10. Prolactin secretion was shown to be TTX-insensitive but sensitive to membrane potential, demonstrated as increased release following increased external K+ but not Na+ concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Corticotropin-releasing factor-producing neurons in the rat activated by interleukin-1

Intraperitoneal administration of human recombinant interleukin-1 (IL-1) to rats can increase blood levels of corticosterone and adrenocorticotropic hormone (ACTH). The route by which IL-1 affects pituitary-adrenal activity is unknown. That the IL-1-induced pituitary-adrenal activation involves an increased secretion of corticotropin-releasing factor (CRF) is indicated by three lines of evidence. First, immunoneutralization of CRF markedly attenuated the IL-1-induced increase of ACTH blood levels. Second, after blockade of fast axonal transport in hypothalamic neurons by colchicine, IL-1 administration decreased the CRF immunostaining in the median eminence, indicating an enhanced release of CRF in response to IL-1. Third, IL-1 did not stimulate ACTH release from primary cultures of anterior pituitary cells. These data further support the notion of the existence of an immunoregulatory feedback circuit between the immune system and the brain.

Complex transcriptional regulation by glucocorticoids and corticotropin-releasing hormone of proopiomelanocortin gene expression in rat pituitary cultures

Proopiomelanocortin (POMC) peptide secretion from rat anterior pituitary corticotrophs and intermediate pituitary melanotrophs is stimulated by corticotropin-releasing hormone (CRH). CRH-stimulated secretion in the corticotrophs is inhibited by glucocorticoids in a complex fashion, involving both a fast, direct blockade of POMC secretion (minutes to hours) and a longer inhibitory action (hours to days) that decreases the amount of POMC peptide available for release. The current studies tested the ability of CRH to stimulate beta-endorphin (a peptide derived from POMC) secretion and POMC gene transcription in cultured anterior and neurointermediate lobe pituitary cells, and examined interactions between CRH and glucocorticoids in regulating POMC gene expression using an in vitro nuclear transcription run-on assay. In both tissues, CRH elicited a time-dependent stimulation of POMC gene transcription that was maximal at 60 min and remained elevated for at least 18 hr. Glucocorticoids rapidly inhibited POMC gene transcription fourfold in the anterior lobe with maximal effects within 20 min. Glucocorticoids also blocked CRH-stimulated POMC gene transcription in anterior pituitary cultures in a temporal manner paralleling their inhibitory effects on CRH-stimulated beta-endorphin secretion. In neurointermediate lobe cultures, the effects of glucocorticoids and CRH on POMC gene transcription were qualitatively similar to, but of lesser magnitude than those observed in the anterior lobe. These studies indicate that the regulation of POMC gene transcription by glucocorticoids and CRH is complex and that the two modulators do not function independently.

Thyroid hormone status regulates preprotachykinin-A gene expression in male rat anterior pituitary

Substance P (SP) and substance K (SK) are mammalian tachykinin peptides derived from a single preprotachykinin-A (PPT-A) gene and are widely but selectively distributed in neural and endocrine tissues. SP is present in the rat anterior pituitary, and its content there varies with the thyroid status of the animal. The present studies were undertaken to determine whether the PPT-A gene is expressed in the anterior pituitary and if so, whether PPT-A messenger RNA (mRNA) abundance is regulated by thyroid hormone status. Male rats were surgically or chemically thyroidectomized or made hyperthyroid by thyroid hormone (T3) injection. Total RNA was isolated from individual anterior pituitaries, and PPT-A mRNA abundance was determined by dot blot procedures. In parallel groups of rats, anterior pituitaries were extracted for measurement of SP and SK by specific RIAs. Surgical or chemical thyroidectomy increased PPT-A mRNA abundance 4 to 6-fold and increased both SP and SK content in the anterior pituitary. Administration of T3 to thyroidectomized rats reversed the increase in both PPT-A mRNA abundance and SP and SK content in the adenohypophysis. T3 administration to euthyroid rats also decreased PPT-A mRNA abundance and SP and SK content in the anterior pituitary. The coordinate presence of PPT-A mRNA with SP and SK in the anterior pituitary strongly suggests that these peptides are synthesized within this gland.

Hormonal regulation of maternal behavior in rats: stimulation following treatment with ectopic pituitary grafts plus progesterone

Changes in hormone secretions during pregnancy help to stimulate the onset of maternal behavior at parturition. To date, studies have demonstrated that estradiol (E2) appears to be a necessary component in the hormonal induction of maternal behavior in rats and other mammals. In the present study, we have reevaluated the contribution of E2, progesterone (P), and hormone-secreting pituitary grafts in the rapid induction of maternal behavior by measuring the behavioral effects of exposure to various combinations of P and prolactin-secreting ectopic pituitary grafts in the absence of estrogen. Adult hypophysectomized and nonhypophysectomized nulliparous rats were ovariectomized 2-3 days (Treatment Day 1) after their arrival in our laboratory. In Experiment #1, experimental, hypophysectomized rats were implanted s.c. with 6 P-filled Silastic capsules and given 2 anterior pituitary (AP) glands that were grafted beneath the kidney capsule on Treatment Day 1. Controls were given blank implants and were sham-grafted. P-filled and blank Silastic capsules were removed on Day 11, and behavioral testing was conducted once-a-day beginning on Day 12 for eleven days. Animals treated with P-plus-pituitary grafts displayed full maternal behavior significantly faster than did controls (median latencies of 3.0 and 7.5 days, respectively). In Experiment #2, nonhypophysectomized rats were assigned to one of three treatments. On Treatment Day 1, one group of rats received 6 P-filled Silastic implants and had 2 AP glands grafted under their renal capsules. A second group of animals received 6 P capsules and was sham-grafted, while controls were given blank implants and were sham-grafted.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological responses to dopamine of rat hypophysial cells in lactotroph-enriched primary cultures

1. Cells from 14-day-old and lactating female rat pituitary glands were dissociated, separated and enriched on a continuous gradient of bovine serum albumin at unit gravity. They were maintained for at least 6 days in culture before perifusion and electrophysiological experiments were performed. 2. Immunofluorescent staining of the resulting gradient fractions (numbered F2 to F9) from both groups of animals indicated that the majority of lactotrophs were located in the light fractions (F3-F4). However, a second population of lactotrophs was observed in the heavy fractions (F7-F9) isolated from lactating females. 3. Basal secretion rates of prolactin were in the order of 2-40 ng 2 min-1 10(6) cells-1 and were inhibited by dopamine in a dose-dependent manner. 4. According to their electrophysiological properties, cells from 14-day-old females (first group) were categorized as follows: (1) inexcitable cells, which displayed a low resting potential of about -35 mV (39% of cells tested, n = 118); and (2) excitable cells, which displayed either triggered or spontaneous action potentials and resting membrane potentials higher than -50 mV (61% of cells tested, n = 185). 5. In the light fraction from lactating females (second group), the majority of the cells were excitable (70%) and showed high resting membrane potentials (-50 to -55 mV) and 15% of these cells displayed spontaneous action potentials. 6. Heavy fractions (third group) contained a high percentage of non-spontaneous but excitable cells (80% of the cells tested, n = 65). These cells were able to elicit action potentials after the cessation of hyperpolarizing current pulses ('off' potentials). 7. Action potentials were insensitive to the sodium channel blocker, tetrodotoxin (TTX; 5 x 10(-6) M) but were reversibly blocked by calcium channel blockers such as cobalt, manganese and cadmium (10 mM). 8. In excitable cells from the three groups, dopamine (10(-7) M) induced a hyperpolarizing response due to an increase of the membrane conductance. During this response, action potentials were inhibited. It was shown that this was not a direct effect of dopamine. The reversal potential of the dopamine-induced response in these cells was found to be at -100 mV. This value was shifted to more positive potentials (-50 mV) when high-potassium medium was used (56 mM). 9. In non-excitable cells (first group), dopamine (10(-7) M) induced a hyperpolarizing response due to a decrease of the membrane conductance.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on hypothalamo-pituitary corticoliberin system. IV. Quantitative changes in ACTH-immunoreactive anterior pituitary cells evoked by long-term intraventricular CRF administration and adrenalectomy

The aim of the study was to investigate, by coupled immunocytochemical and stereologic methods, the effects of long-term intraventricular administration of ovine CRF (oCRF) on ACTH-immunoreactive cells of the rat anterior pituitary and to compare this effect with that of adrenalectomy. CRF-treated rats received 100 ng of oCRF daily for 8 days while control rats were administered with bovine serum albumin (BSA). After BSA administration number of ACTH-immunoreactive cells/mm2 was greater than in intact rats and CRF lowered their number, however, they were still more numerous than in intact rats. Neither average area nor average volume of studied cells were changed in control and CRF-treated animals if compared with intact ones. The total number of ACTH-immunoreactive cells was higher in the glands of BSA and CRF-treated rats than in intact animals. On the other hand, 60 h after bilateral adrenalectomy a marked increase in both, average area and average volume of ACTH-immunoreactive cells was found. The different response of rat corticotropes to intraventricular CRF administration and adrenalectomy may depend on the presence of operating negative corticosterone feedback in animals with adrenal glands intact. Moreover, the present study revealed the lack of correlation between the average area and average volume of ACTH-immunoreactive cells and the weight of the adrenal gland.

Direct inhibitory effect of long term estradiol treatment on dopamine synthesis in tuberoinfundibular dopaminergic neurons: in vitro studies using hypothalamic slices

The mechanism of the inhibitory effect of long term treatment with estradiol on dopamine synthesis in tuberoinfundibular dopaminergic (TIDA) neurons was studied by using hypothalamic slices from ovariectomized rats. Treatment with 2 mg estradiol valerate (EV) at a 3-week interval increased the weight of the anterior pituitary gland and the concentration of serum PRL. In vivo and in vitro dopamine synthesis in TIDA neurons were estimated in EV-treated animals by 3,4-dihydroxyphenylalanine (DOPA) accumulation in the median eminence after injections of 3-hydroxybenzylhydrazine (NSD 1015), a DOPA decarboxylase inhibitor, and after incubation of hypothalamic slices with NSD 1015, respectively. In vivo DOPA accumulation in the median eminence was less in EV-treated rats than in control rats. The basal rate of in vitro DOPA accumulation in the median eminence of hypothalamic slices from EV-treated rats was lower than that in control rats. Ca2+-dependent DOPA accumulation in the median eminence, determined by incubation in medium containing depolarization agents such as 50 mM K+ and veratridine, was decreased in EV-treated rats. Furthermore, cAMP-dependent DOPA accumulation, determined by incubation with Bu2cAMP or forskolin, was also suppressed in EV-treated rats. The decreased depolarization-induced DOPA accumulation in the median eminence recovered after cessation of EV treatment. Hyperprolactinemia lasting for 6 weeks, achieved by transplantation of anterior pituitaries under the kidney capsule, increased the rate of depolarization-induced DOPA accumulation in the median eminence. On the other hand, EV treatment was effective in inhibiting depolarization-induced DOPA accumulation in hypophysectomized rats regardless of the presence of anterior pituitary transplants. These results suggest that chronically administered estradiol inhibits dopamine synthesis in TIDA neurons via a direct action on the hypothalamus and overcomes the facilitatory action of PRL on dopamine synthesis; and estradiol inhibits all three distinct systems that regulate basal, Ca2+-dependent, and cAMP-dependent dopamine synthesis in TIDA neurons.

Hypothalamic secretion of thyrotropin releasing hormone declines in aging rats

Young and aged male rats were used in experiments to investigate a possible decline in hypothalamic secretion of thyrotropin releasing hormone (TRH) to the anterior pituitary of aging mammals. We observed a 66% decrease in basal TRH release by incubated rat hypothalami with aging. Thyroid hormone-responsive hepatic alpha-glycerophosphate dehydrogenase (GPD) and malic enzyme (ME) levels in aged rats did not differ from 5-month-old controls in spite of a significant fall in serum thyroxine (T4) levels with aging. Other results suggest that these particular indicators of thyroidal status should not change in the aging rat because serum T3 is maintained in the normal range. Serum thyrotropin (TSH) levels, which normally rise when serum T4 levels decline, did not change with aging. These data suggest that gradual loss of the essential TRH stimulation of TSH release with aging may be compensated for by a decline in T4 inhibition of TSH release at the pituitary.