Characterization of gonadotropic cells during continuous and seasonal spermatogenesis of two freshwater fish species: a histochemical and immunohistochemical study.

This work describes gonadotropic (GtH) cells and their morphological and immunohistochemical changes during the spermatogenic cycle of Serrasalmus maculatus (continuous spermatogenesis) and Pimelodus maculatus (seasonal spermatogenesis). GtH cells, widely distributed in the proximal pars distalis of the adenohypophysis, were characterized as round-shaped cells with eccentric nucleus, and cytoplasm with basophilic secretory granules and a variable number of vacuoles for both species. Immunohistochemistry against ß-follicle-stimulating hormone (Fsh) and ß-luteinizing hormone (Lh) in adjacent sections showed two separated GtH-producing cell populations, and a third population where both GtHs are expressed in the same cell for both species. In the seasonal spermatogenesis of P. maculatus, GtH cells seemed to be more abundant during developing and spawning capable phases. In contrast, no cyclic changes were detected in the continuous spermatogenesis of S. maculatus, except for the strong immunoreaction for Fsh and Lh in males with intense spermiogenesis. We conclude that changes reported here might reflect the type of spermatogenic cycle (seasonal or continuous) which are under different regulatory mechanisms (environmental and internal cues) controlling the reproduction in these species.

Related pituitary cell lineages develop into interdigitated 3D cell networks.

The pituitary gland has long been considered to be a random patchwork of hormone-producing cells. By using pituitary-scale tridimensional imaging for two of the least abundant cell lineages, the corticotropes and gonadotropes, we have now uncovered highly organized and interdigitated cell networks that reflect homotypic and heterotypic interactions between cells. Although newly differentiated corticotrope cells appear on the ventral surface of the gland, they rapidly form homotypic strands of cells that extend from the lateral tips of the anterior pituitary along its ventral surface and into the medial gland. As the corticotrope network is established away from the microvasculature, cell morphology changes from rounded, to polygonal, and finally to cells with long cytoplasmic processes or cytonemes that connect corticotropes to the perivascular space. Gonadotropes differentiate later and are positioned in close proximity to corticotropes and capillaries. Blockade of corticotrope terminal differentiation produced by knockout of the gene encoding the transcription factor Tpit results in smaller gonadotropes within an expanded cell network, particularly in the lateral gland. Thus, pituitary-scale tridimensional imaging reveals highly structured cell networks of unique topology for each pituitary lineage. The sequential development of interdigitated cell networks during organogenesis indicate that extensive cell:cell interactions lead to a highly ordered cell positioning rather than random patchwork.

Cytodifferentiation of Wulzen's cone of mature male sheep hypophysis cerebri with special emphasis on its parenchymal correlations with the adjacent pars distalis, pars intermedia and pars nervosa.

Background: Hypophysis cerebri is considered the master endocrine gland as it plays a critical role in influencing and controlling the vitality of other endocrine organs via several hormones secretion. Aim: The present study was performed to clarify the localization of Wulzen's cone (WC) within sheep hypophysis and cytodifferentiation of the glandular cells filling cone parenchyma with particular emphasis on the cone correlations with adjacent pars distalis (pd), pars intermedia (pi), and pars nervosa (pn). Methods: Pituitaries were collected and processed histologically, then subjected to different combinations of special stains; Br-AB- OFG., PFA-AB-PAS-OG., PAS-Orange G., Orange G- Acid Fuchsin- Light Green, Bielschowsky technique, Masson's trichrome & Gomori's reticulin. Results: A sagittal section through the pituitaries revealed a well-developed cone of glandular cells protruding from the pi like a tongue plate towards the hypophyseal cleft in the neighborhood of the pd and behind the pn. Resembling the pd, various glandular cells were distinguished in the cone; chromophobes and chromophils of acidophils & basophils. The cone is mainly formed from acidophils intermingled with the chromophobes. Meanwhile, basophils were primarily localized at the most anterior & posterior parts of the cone. In front of the cone, pd were localized, resembling a wing-shaped and filled with several categorized glandular cells; chromophobes and chromophils. Upper to the cone, pi were localized and composed mainly of weakly basophilic cuboidal or polygonal cells arranged in parallel cords or follicles. Behind the cone, pn was localized as a ventral outpouching of the brain floor-like water drop. Unlike the cone, it was devoid of any glandular secretory cells or nerve cells but consisted mainly of unmyelinated nerve fibers, herring bodies, and pituicytes. Conclusion: WC is present and well-developed in sheep adenohypophysis. Various glandular cells were distinguished, filling the cone, chromophobes, and chromophils of acidophils & basophils that were typically similar to the glandular cells of pd but with different distributions.

Structural characteristics of adenohypophysis in hypertensive ISIAH rats in early ontogeny.

Comparative morphological study of the adenohypophysis was conducted in 3-week-old normotensive WAG and hypertensive ISIAH rats (prehypertension period) to elucidate the role of the adenohypophysis in the development of essential hypertension. Morphometric analysis revealed ultrastructural signs of functional activation of somatotrophs, gonadotrophs, and corticotrophs in ISIAH rats. These peculiarities of structural organization of adenohypophysis in hypertensive rats can attest to enhanced response of the hypothalamic-pituitary-adrenal axis in these animals to natural stress associated with their transition to independent feeding. Increased stress sensitivity during the prehypertensive period of postnatal ontogeny contributes to the development of arterial hypertension.

Associations between early life stress and anterior pituitary gland volume development during late childhood.

Early Life Stress (ELS) is thought to influence Hypothalamic-Pituitary-Adrenal-Axis (HPAA) functioning, contributing to an increased risk for psychopathology through dysregulation of biological stress responses. Research exploring relationships between ELS and HPAA functioning has largely focused on its key hormonal output, cortisol. However, findings have been inconsistent, potentially due to cortisol's distinctive diurnal patterns and dynamic nature complicating its accurate measurement. Thus, this study explored the link between ELS and a more stable, structural component of the HPAA, specifically, anterior pituitary gland volume (PGV) in a community sample of children (N = 129, 68 female). PGV was traced from Magnetic Resonance Imaging brain scans across two time-points at ages 8 (baseline) and 10 years (follow-up). ELS exposure was assessed at baseline through parent-report questionnaires and maternal affective behavior observed in mother-child interaction tasks. ELS variables were reduced to a 5-factor structure using exploratory factor analysis - Uninvolved Parenting, Negative Affective Parenting, Neglect, Trauma, and Dysfunctional Discipline. Direct and sex-moderated associations between ELS and PGV were explored using regression and linear mixed models analyses. PGV-mediated associations between ELS and internalizing symptoms were also investigated. Childhood Neglect was significantly associated with greater baseline anterior PGV, that was stable over the follow-up period. This effect was found in the whole sample, and in males, specifically. No mediation effects were found. Results suggest that neglect may play a unique role in HPAA neurodevelopment; however, it is important that future research extends into adolescence to more clearly characterize these neurodevelopmental associations and any subsequent psychopathological outcomes.

Immunocytochemical identification of adenohypophyseal cells in the pirarucu (Arapaima gigas), an Amazonian basal teleost.

The adenohypophysis (AH) of juvenile pirarucu (Arapaima gigas), a representative species of the Osteoglossomorpha (bonytongue fishes, one of the oldest living groups of the teleosts), was studied using histochemical and immunocytochemical methods. The AH is comprised of the pars distalis (PD), without a clear distinction between rostral pars distalis (RPD) and proximal pars distalis (PPD), and the pars intermedia (PI). The neurohypophysis (NH) is positioned on top of the PD and penetrates and branches into the PI. In the most rostral dorsal portion of the PD, adrenocorticotropic cells and fusiform gonadotropic cells were found. In the central PD, scarce prolactin-producing cells and growth-hormone-producing cells were located mainly in the dorsal part, whereas round gonadotropic cells were abundant in the ventral portion of this region. Human thyrotropin immunoreactive cells were not found in the entire AH. In the PI, melanotropic, some adrenocorticotropic, and somatolactin-producing cells were located intermingled surrounding the neurohypophyseal branches. Our results showed that the A. gigas pituitary has some basal characteristics between the ancient Actinopterygii and the more derived teleosts.

Localization of calcium-binding protein (calretinin, 29 kD) in the brain and pituitary gland of teleost fish: an immunohistochemical study.

Immunocytochemical techniques were used to investigate the distribution of calretinin in the brain and pituitary gland of the hardhead catfish Arius felis. Calretinin immunoreactive neurons were found in the telencephalon (lateral nucleus of ventral telencephalic area), diencephalon (around the medial forebrain bundle, lateral tuberal nucleus, central pretectal nucleus, posterior periventricular hypothalamic nucleus, medial preglomerular nucleus, diffuse nucleus of the inferior lobe), mesencephalon (nucleus of the medial longitudinal fascicle, ventral nucleus of the semicircular torus), cerebellum (valvula cerebelli, eurydendroid cells) and rhombencephalon (secondary gustatory nucleus, isthmic nucleus, trigeminal motor nucleus, medial auditory nucleus of the medulla, medial and inferior reticular formation, anterior, descending, posterior and tangential octaval nuclei). Calretinin-labeled fibers were observed in the optic nerve and at the levels of the central pretectal nucleus, the nucleus of the medial longitudinal fascicle, the ventral nucleus of the semicircular torus, the secondary gustatory nucleus, the trigeminal motor nucleus, the eurydendroid cells, the medial auditory nucleus of the medulla and the octaval nucleus. For the first time, we are reporting on calretinin-positive cells in the rostral and proximal pars distalis of the adenohypophysis. Although, it seems speculatory, calretinin-expressing cells in the pituitary gland may be involved in hormonal regulation and hence, calretinin might play a significant role in governing hypophysial functions in fishes. Our results suggest that calretinin shows species-specific variations also among the teleost fish, similar to mammals.

Plurihormonal cells of normal anterior pituitary: Facts and conclusions.

INTRODUCTION: plurihormonality of pituitary adenomas is an ability of adenoma cells to produce more than one hormone. After the immunohistochemical analysis had become a routine part of the morphological study, a great number of adenomas appeared to be multihormonal in actual practice. We hypothesize that the same cells of a normal pituitary gland releases several hormones simultaneously. OBJECTIVE: To analyse a possible co-expression of hormones by the cells of the normal anterior pituitary of adult humans in autopsy material. MATERIALS AND METHODS: We studied 10 pituitary glands of 4 women and 6 men with cardiovascular and oncological diseases. Double staining immunohistochemistry using 11 hormone combinations was performed in all the cases. These combinations were: prolactin/thyroid-stimulating hormone (TSH), prolactin/luteinizing hormone (LH), prolactin/follicle-stimulating hormone (FSH), prolactin/adrenocorticotropic hormone (ACTH), growth hormone (GH)/TSH, GH/LH, GH/FSH, GH/ACTH, TSH/LH, TSH/FSH, TSH/ACTH. Laser Confocal Scanning Microscopy with a mixture of primary antibodies was performed in 2 cases. These mixtures were ACTH/prolactin, FSH/prolactin, TSH/prolactin, ACTH/GH, and FSH/GH. RESULTS: We found that the same cells of the normal adenohypophysis can co-express prolactin with ACTH, TSH, FSH, LH; GH with ACTH, TSH, FSH, LH, and TSH with ACTH, FSH, LH. The comparison of the average co-expression coefficients of prolactin, GH and TSH with other hormones showed that the TSH co-expression coefficient was significantly the least (9,5±6,9%; 9,6±7,8%; 1,0±1,3% correspondingly). CONCLUSION: Plurihormonality of normal adenohypophysis is an actually existing phenomenon. Identification of different hormones in pituitary adenomas enables to find new ways to improve both diagnostic process and targeted treatment.

Immunohistochemical study of somatotrophs in pituitary pars distalis of male viscacha (Lagostomus maximus maximus) in relation to the gonadal activity.

Somatotrophs were identified and quantified in pituitary pars distalis of male viscachas (Lagostomus maximus maximus) during the annual reproductive cycle, after the administration of melatonin, after castration and in different growth stages by immunohistochemistry and morphometric analysis. In adult male viscachas, the somatotrophs were distributed throughout the pars distalis during the reproductive cycle. They were oval, pyramidal or round in shape with a large round nucleus. The percentage immunopositive area, the major cellular diameter and the number of cells decreased during the gonadal regression period in relation to the values found in the reproductive period. The administration of melatonin did not provoke any variations of the morphometric parameters studied. On the contrary, a significant decrease in the percentage immunopositive area, in the major cellular diameter and in the number of somatotrophs in castrated viscachas was observed. The study of different growth stages showed that these morphometric parameters increased from immature to adult animals in the reproductive period. The results obtained suggested that the variations of the morphometric parameters of somatotrophs are more related to the gonadal development and activity than to a direct effect of melatonin.

Three-dimensional ultrastructural analyses of anterior pituitary gland expose spatial relationships between endocrine cell secretory granule localization and capillary distribution.

Endocrine and endothelial cells of the anterior pituitary gland frequently make close appositions or contacts, and the secretory granules of each endocrine cell tend to accumulate at the perivascular regions, which is generally considered to facilitate secretory functions of these cells. However, three-dimensional relationships between the localization pattern of secretory granules and blood vessels are not fully understood. To define and characterize these spatial relationships, we used scanning electron microscopy (SEM) three-dimensional reconstruction method based on focused ion-beam slicing and scanning electron microscopy (FIB/SEM). Full three-dimensional cellular architectures of the anterior pituitary tissue at ultrastructural resolution revealed that about 70% of endocrine cells were in apposition to the endothelial cells, while almost 30% of endocrine cells were entirely isolated from perivascular space in the tissue. Our three-dimensional analyses also visualized the distribution pattern of secretory granules in individual endocrine cells, showing an accumulation of secretory granules in regions in close apposition to the blood vessels in many cases. However, secretory granules in cells isolated from the perivascular region tended to distribute uniformly in the cytoplasm of these cells. These data suggest that the cellular interactions between the endocrine and endothelial cells promote an uneven cytoplasmic distribution of the secretory granules.

Hypothalamo-pituitary-adrenal gland axis in mice inhaling toluene prior to low-level long-term exposure to formaldehyde.

We studied the change in the hypothalamo-pituitary-adrenal gland (HPA) axis upon adding prior toluene inhalation to our previous formaldehyde inhalation experiments to determine whether short term exposure to relatively high levels of toluene triggers multiple chemical sensitivity (MCS). Data come from immunocytochemical, morphometrical and RT-PCR measurements. Four groups of adult female mice were exposed to differing concentrations (0, 80, 400, and 2,000 ppb) of formaldehyde for 16 hr/day, 5 days/week for twelve weeks, after the mice were exposed intranasally to 500 ppm toluene per mouse for 6 hr/day, for 3 days. We found that the number of corticotropin releasing hormone (CRH)-immunoreactive (ir) neurons was up-regulated according to the amount of formaldehyde as well as inhalation of formaldehyde alone in our previous experiment. The proportion of adrenocorticotropin hormone (ACTH)-ir cells increased according to the formaldehyde concentration, though there was no significant difference between the 400 and 2,000 groups. The number of ACTH-ir cells was higher in the 400 group than in the other groups (0, 80, and 2,000). Expression of ACTH-mRNA was also up-regulated according to the quantity of formaldehyde. The sinusoid in the anterior pituitary showed more dilatation in the 400 and 2,000 groups than in the control group, especially in the 2,000 group. We propose that exposure to toluene prior to inhalation of formaldehyde has no effect on the HPA axis and as a trigger of MCS, although greater sinusoid dilatation was found in the anterior pituitary gland at higher concentrations of formaldehyde.

A membranous structure separating the adenohypophysis and neurohypophysis: an anatomical study and its clinical application for craniopharyngioma.

OBJECT This study aimed to identify the membranous septation between the adeno- and neurohypophysis. The clinical impact of this septation in the surgical removal of infradiaphragmatic craniopharyngioma (Id-CP) is also clarified. METHODS The sellar regions from 8 fetal and 6 adult cadavers were dissected. After staining first with H & E and then with picro-Sirius red, the membranous structures were observed and measured under normal light and polarization microscopy. The pre- and postsurgical images and intraoperative procedures in 28 cases of childhood Id-CP were reviewed and analyzed. RESULTS There is a significant membranous septation (termed the adenoneurohypophysis septation [ANHS]) lying behind the intermediate lobe to separate the adeno- and neurohypophysis. The average thicknesses are 21.9 ± 16.9 µm and 79.1 ± 43.2 µm in fetal and adult heads, respectively. The median segment of the septation is significantly thicker than the upper and lower segments. The ANHS extends from the suprasellar pars tuberalis to the sellar floor, where it is fused with the pituitary capsule. During Id-CP surgery performed via a transcranial approach, the ANHS can be identified to reserve the neurohypophysis. Moreover, by understanding the anatomy of this membrane, the pituitary stalk was preserved in 3 patients (10.7%). CONCLUSIONS There is a significant membrane separating the anterior and posterior lobes of the pituitary gland, which lies behind the intermediate lobe. Understanding the anatomy of this septation is important for identifying and preserving the neurohypophysis and pituitary stalk during Id-CP surgery.

Morphometric analysis of somatotropic cells of the adenohypophysis and muscle fibers of the psoas muscle in the process of aging in humans.

The aim of this research was to quantify changes of the adenohypophyseal somatotropes and types 1 and 2 muscle fibers with aging, as well as to establish mutual interactions and correlations with age. Material was samples of hypophysis and psoas major muscle of 27 cadavers of both genders, aged from 30 to 90 years. Adenohypophyseal and psoas major tissue sections were immunohistochemically processed and stained by anti-human growth hormone and anti-fast myosin antibodies, respectively. Morphometric analysis was performed by ImageJ. Results of morphometric analysis showed a significant increase in the somatotrope area, and significant decrease in somatotrope volume density and nucleocytoplasmic ratio with age. Cross-sectional areas of types 1 and 2, and volume density of type 2 muscle fibers decreased significantly with age. One Way ANOVA showed that the latter cited changes in the somatotropes and types 1 and 2 muscle fibers mostly become significant after the age of 70. Significant positive correlation was observed between the area of the somatotropes and volume density of type 2 muscle fibers. A significant negative correlation was detected between the nucleocytoplasmic ratio of the somatotropes and cross-sectional areas of types 1 and 2 muscle fibers. So, it can be concluded that after the age of 70, there is significant loss of the anterior pituitary's somatotropes associated with hypertrophy and possible functional decline of the remained cells. Age-related changes in the somatotropes are correlated with the simultaneous atrophy of type 1, as well as with the atrophy and loss of type 2 muscle fibers.

Prolactin secretion after hypophysial stalk transection in pigs.

Hypothalamic regulation PRL secretion was investigated in 13 7-month-old Yorkshire gilts by comparing the effects of hypophysial stalk transection and sham operation. Ovariectomized gilts were fitted with an indwelling cannula in the anterior vena cava to determine sequential serum profiles of PRL secretion before, during, and 190 h after cranial surgery. A nylon disc was inserted between severed ends of the hypophysial stalk to prevent vascular and tissue regeneration; sham operations included all surgical procedures with exception of stalk transection and insertion of the disc. During a preoperative period of 120 min, PRL concentrations in peripheral serum remained consistently low [2.3 +/- 0.3 ng/ml (mean +/- SEM)] in all gilts. During 105 min of anesthesia (induced by thiamylal sodium and maintained by halothane and oxygen), PRL increased (8.2 +/- 1.9 ng/ml) in all gilts. Peak PRL values averaged 10.7 ng/ml at hypophysial stalk transection or sham operation and then declined steadily in both groups during the last 105 min of surgery. PRL remained elevated (P less than 0.002) in hypophysial stalk-transected gilts compared with sham-operated controls throughout a postoperative period from 6-190 h (3.7 +/- 0.4 vs. 1.9 +/- 0.2 ng/ml). These results indicate that basal secretion of PRL in the pig is inhibited by the hypothalamus.

Alterations in the secretion and production of follicle-stimulating hormone precede age-related lengthening of estrous cycles in rats.

The present study evaluated the effects of aging on the hormone profile of FSH as well as that of LH and PRL during proestrus (P) and estrus (E) of the 4-day rat estrous cycle. Furthermore, in view of the heterogeneity of FSH forms in the anterior pituitary gland (AP), we also sought to ascertain the effects of aging on the type of FSH produced by the AP. An attempt then was made to correlate possible changes in the synthesis and/or release of FSH with the initial decline in the incidence of regular 4-day estrous cycles in our colony of rats. Virgin rats aged 3, 5, 7, and 9 months, exhibiting 4-day estrous cycles were outfitted with atrial cannulae on proestrous morning. Blood samples were obtained every 4 h from 1400 h on P to 1000 h on E. At 1600 h on E, all rats were killed, trunk blood was collected, and the AP was removed, weighted, and homogenized. The concentrations of FSH, LH, and PRL in plasma and AP supernatant were determined by RIA, while the analysis of FSH isohormones in the remaining supernatant was made by chromatofocusing. At 3 and 5 months of age, 74% and 62% of the rats exhibited regular 4-day estrous cycles, respectively. This percentage had declined to 35% at 7 months and to 16% by 9 months of age. The marked decline in the incidence of 4-day cycles between 5 and 7 months was accompanied by an increased incidence of 5- to 7-day cycles, while by 9 months of age, 38% of the rats exhibited persistent vaginal cornification. In comparison to 3-month-old rats, plasma FSH levels were higher in 5-month-old rats at 1400 h on P and 1600 h on E. By 7 months, not only were plasma FSH levels increased further at these times, but they also were increased at 0600 and 1000 h on E during the secondary FSH surge. By 9 months, the preovulatory FSH surge appeared to be delayed, and the characteristic biphasic elevation in FSH levels on P and E was absent. In contrast to FSH, no change in the profile of plasma LH levels occurred until 9 months, when there was a marked reduction in the magnitude of the preovulatory LH surge. PRL levels were not consistently altered with age.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormone secretion in genetic large (LL) and small (SS) rats.

We investigated whether genetic selection for growth influences pituitary GH secretion in two strains of rats, LL (large) and SS (small). Animals were bled every 15 min for 6 h via an indwelling atrial Silastic catheter, and GH levels were determined by RIA. LL and SS males displayed a low frequency, high amplitude episodic pattern of GH secretion, with surges of GH occurring at 3- to 4-h intervals, separated by trough periods of approximately 60-120 min. In contrast, LL females showed a high frequency, low amplitude pattern of GH secretion, with GH pulses occurring every 1-2 h. The number of GH pulses in SS females was lower than that in LL females. SS males and SS females displayed lower peak amplitudes and lower baseline levels and, therefore, lower mean plasma GH levels compared to LL animals. The anterior pituitary GH content was not significantly different in LL and SS animals of either sex. Thus, the reduction of GH levels in SS animals is most likely the result of reduced release of GH-releasing factor from the hypothalamus or an attenuated pituitary sensitivity to GH-releasing factor.

Early short photoperiod effects in female LSH/SsLak Syrian hamsters.

Previous experiments showed that LSH/SsLak female hamsters cease ovarian cyclicity after 2-4 weeks of short photoperiod (SP) treatment. This study was designed to reveal early hormonal and histological changes on day 1 of the estrous cycle (estrus) in SP-treated animals and changes brought about by the SP-induced acyclic condition. Groups of 8-10 animals were killed on day 1 after 0, 4, 8, 12, and 16 days of SP treatment; sera and pituitaries were saved for hormone determinations, and ovaries were prepared for histological analysis. Intraatrial cannulae were inserted into anovulatory animals, and blood samples were withdrawn on the first and second postoperative days; the animals were killed on the third postoperative day. PRL levels were significantly reduced in cycling animals after 16 days of SP exposure and diminished further in acyclic animals. Pituitary PRL did not change in cycling animals, although it was highly depressed in SP-treated acyclic animals. The estrous FSH surge, serum LH levels, and pituitary gonadotropin contents were not affected by SP in cycling animals; in anovulatory animals, pituitary gonadotropin contents were significantly increased, and daily afternoon gonadotropin surges were observed. Uterine weights were reduced in cycling animals and underwent a further reduction after cyclicity ceased. Ovarian analysis revealed that all cycling animals had the same number of recruited follicles, yet significantly fewer corpora lutea and an apparent increase in atretic antral follicles were observed after 16 days of SP exposure. These results suggest that SP-induced cessation of estrous cyclicity occurs abruptly. SP does not alter the secondary FSH surge, but might adversely affect maintenance of follicular growth and depress serum PRL levels.

Growth hormone releasing activity of thyrotropin-releasing hormone in rats with hypothalamic lesions.

The growth hormone (GH)-releasing effect of thyrotropin-releasing hormone (TRH) was investigated in rats in which central nervous system (CNS)-anterior pituitary (AP) connections had been experimentally interrupted. Sprague-Dawley (SD) female and male rats, underwent bilateral electrolytic lesions in the median eminence (ME) or the ventromedial nuclei (VMN) or were sham-operated (sham-op). Fifteen days after surgery, 0.9% NAACl or TRH was injected iv into sham-op rats or those with lesions in the CNS, anesthetized with urethane, and blood was drawn at 5 and 10 min posttreatment. In the rats with ME lesions, TRH at all the doses used (0.1, 0.4 and 0.8 microng/100 g BW) induced a marked, although not dose-related GH rise, which was not present in sham-op rats after TRH, or after NaCl administration to either rats with ME lesions or sham-op rats. In SD male rats lesioned in the VMN, TRH at doses of 0.4 and 0.8 microng/100 g BW induced significant GH rises, while the lowest TRH dose (0.1 microng/100 g BW) was ineffective; again, TRH was ineffective at all doses used in sham-op rats. Concomitant evaluation of the prolactin (PRL)-releasing effect of TRH (0.1-0.8 microng/100 g BW), showed a striking elevation of plasma PRL in both female and male sham-op controls, but no PRL rise in the rats with ME lesions. The results reveal that in the rat with surgical separation of the anterior pituitary from the CNS, a direct GH-releasing effect of TRH can be obtained, whereas its PRL-releasing effect is no longer observed, and suggest that, by analogy, the GH-releasing effect of TRH present in some disease states of the human may be due to an impairment of CNS-AP connections.

Reduction of lactogenic receptors in female hamster liver due to the human growth hormone analog produced by plerocercoids of the tapeworm, Spirometra mansonoides.

The inductive effect of GH on hepatic lactogenic receptors is suspected of being due to a direct somatogenic action. Plerocercoid larvae of the tapeworm, Spriometra mansonoides, produce a factor that stimulates body growth, suppresses endogenous GH, and specifically displaces [125I]human (h) GH from hepatic receptors. Plerocercoid growth factor (PGF) mimics the growth-promoting actions of GH, but it has not been shown to duplicate all of the activities reported for GH. An important function of GH is its role in the maintenance of liver receptors for lactogenic hormones. This study was undertaken to determine if treatment of female hamsters with PGF would increase, decrease, or have no effect on liver receptors that bind hGH. Since hGH binds to somatogenic as well as lactogenic receptors, it was necessary to demonstrate the specificity of PGF's effects on [125I]hGH binding. PGF-treated (15 pleocercoids sc) hamsters had accelerated body growth, suppressed serum GH, and a marked reduction in [125I]hGH and [125I]ovine PRL binding to hepatic microsomes. Specific binding of [125I] bGH was unaltered by PGF treatment. The difference in [125I] hGH binding was due to a reduction in receptor number and not to receptor occupancy or reduced affinity. Serum GH was normalized after 10 days of estradiol benzoate (25 micrograms/day) injections, but the binding capacity for [125I]hGH of the PGF-treated group was less than half that of the control group. The fact that estrogen injections normalized serum GH, but not hGH binding, indicates that down-regulation of these receptors by PGF cannot be entirely explained on the basis of reduced levels of serum GH. The lack of any effect of PGF treatment on [125I]bGH binding suggests that the hepatic somatogenic receptors were not involved and that the reduction in receptors for [125I]hGH was associated with the lactogenic component of hGH.

Functional variations among prolactin cells from different pituitary regions.

Reverse hemolytic plaque assays were used to compare the responsiveness of cells from different pituitary regions to the modulatory effects of human pancreatic GH-releasing factor (GRF), TRH, and dopamine (DA). Tissues from the peripheral rim (outer zone) and the central region (inner zone) of adenohypophyses from day 10 lactating rats were dispersed with trypsin, and the cells were placed into culture. On the following day, these cells were subjected to GH plaque assays (conducted in the presence or absence of GRF) and PRL plaque assays (performed with or without TRH and DA). Cells from both zones responded similarly to GRF with a rapid acceleration of GH plaque formation. However, the rate of PRL plaque formation in response to TRH and DA differed between cells from these regions. For outer zone cells, plaque development increased greatly with TRH treatment, but was only moderately affected by DA. Plaque formation from inner zone cells was influenced slightly by TRH, but markedly inhibited by DA. These results suggest that PRL, but not GH, cells from these pituitary regions are differentially responsive to at least two hypothalamic secretagogues. We then performed fixed sequential plaque assays to determine whether the proportions of cells that released PRL only (classical mammotropes) or those that released both GH and PRL (mammosomatotropes) also differed between the inner and outer zones. Using this approach, we found that the outer zone contained a much larger proportion of dual hormone secretors than did the inner zone. These results, when taken together with the responsiveness differences discussed above, raise the possibility that the release of PRL from mammotropes and mammosomatotropes is regulated differently and that the ratio of these two cell types may dictate, in part, the manner in which a specific region of the pituitary responds to hypothalamic input.