Cytological changes of the pituitary basophils in rats slowly infused with LRH and with LRH and THR in combination.

Young male rats were iv infused with synthetic LRH (L) and with L and TRH (T) in combination for 1, 3, 24, 48 and 72 hrs at each dose of 1 microgram/hr. All the basophils of the controls infused with saline are divided into the continuous cyclic types, i.e., II-, II/III, III-, III/IV- and III/IV/II-types. The II-, III- and III/IV-type cells correspond, in fine structure, with those of the classical thyrotrophs, LH- and FSH-gonadotrophs, respectively. A 1-hr infusion of L does not induce any serious changes in all the basophils. After a 3-hr infusion of L, the II-type cells disperse from the gland, while the III/IV-type cells diminished the number of their small secretory granules, and the lumina of endoplasmic reticulum are closed. After a 24-hr infusion, the irregularly shaped III/IV/II-type cells which may revert from the III/IV- to the II-type cells are accumulated, whose secretory granules are remarkably reduced in diameter (50--100 nm). There is evidence to show the diffusion mechanism of the secretory granules into the ground matrix. After a 48-hr infusion of L, most basophils take an appearance of III/IV/II-type cells; after a 72-hr infusion, all the basophils show the homologous fine structure. Thus, the morphological changes of the basophils following the L infusion resemble intrinsically those following the T infusion (Soji, 1976b). From these results, it is tentatively concluded that L does not act only on the III-type cells analogous to the "LH-cells", but universally upon a series of basophils. The transformations of the III/IV-type cells into the III/IV/II-type ones and those of the II-type ones into the III- or III/IV-type ones due to a slow infusion of L are inhibited to some extent by the infusion of T + L. The granular releases from the III/IV- and II-type cells due to a slow infusion of L are also inhibited to some extent by the infusion of T + L. For this reason, both T and L may act, not synergistically but antogonistically, upon the transformation of a series of basophils and their granular release.     

Secretory morphology of the intermediate lobe of the rat pituitary incubated in vitro

Summary The ultrastructure of the incubated intermediate lobe of the rat pituitary and the morphological effect of isoproterenol stimulation on its cells were studied under in vitro conditions. The general structure of isolated neurointermediate lobes maintained for 2–3 h in vitro was well preserved, and the presence of intact nerve terminals establishing synaptic contacts with the glandular cells of the intermediate lobe was confirmed. Removal of the intermediate lobe from central inhibition leads to increased hormonal secretion, which was reflected by large Golgi areas and the appearance of secretory images. However, no obvious degranulation or peripheral migration of the secretory granules after 2–3 h in vitro was seen. The secretory granules varied in electron density; totally electron-lucent granules were regularly observed and exocytotic phenomena were shown. In addition, more extensive invaginations suggesting secretion by compound exocytosis were seen. A three-fold increase in the -endorphin secretion during a 4-min stimulation with 10^-6 M isoproterenol did not induce any morphometrically detectable changes in the incubated cells. This indicates that only a minor fraction of the total granule content is mobilized during an acute increase in secretory activity.     

Secretory plasticity of pituitary cells: a mechanism of hormonal regulation

Pituitary somatotropes and melanotropes have enabled us to investigate the molecular basis and functional dynamics underlying secretory plasticity, an ability of endocrine cells to adapt their activity to the changing physiologic requirements, which generates discrete cell subpopulations within each cell hormonal type. Porcine somatotropes comprise two morphologically distinct subpopulations of low- (LD) and high-density (HD) cells, separable by Percoll gradient, that respond differently to hypothalamic regulators. In LD somatotropes, somatostatin (SRIF) inhibits growth hormone (GH)-releasing hormone (GHRH)-induced GH secretion. Conversely, SRIF alone stimulates GH release from HD somatotropes. These disparate SRIF actions entail a molecular signaling heterogeneity, in that SRIF increases cAMP levels in HD but not in LD cells as a requisite to stimulate GH release. GHRH-stimulated GH release also involves differential signaling in LD and HD cells: although it acts primarily through the cAMP/extracellular Ca2+ route in both somatotrope subsets, full response of LD somatotropes also requires the inositol phosphate/intracellular Ca2+ pathway. Amphibian melanotropes, which regulate skin adaptation to background color by secreting POMC-derived alpha-melanocyte-stimulating hormone (alphaMSH), also comprise two subpopulations with divergent secretory phenotypes. LD melanotropes show high biosynthetic and secretory activities and high responsiveness to multiple hypothalamic factors. Conversely, HD melanotropes constitute a hormone-storage subset poorly responsive to regulatory inputs. Interestingly, in black-adapted animals most melanotropes acquire the highly-secretory LD phenotype, whereas white-background adaptation, which requires less alphaMSH, converts melanotropes to the storage HD phenotype. These same interconversions can be reproduced in vitro using appropriate hypothalamic factors, thus revealing the pivotal role of the hypothalamus in regulating the functional dynamics of the secretory plasticity. Furthermore, this regulation likely involves a precise control of the secretory pathway, as suggested by the differential distribution in LD and HD melanotropes of key components of the intracellular transport, processing, and storage of secretory proteins. Hence, molecular signaling heterogeneity and unique secretory pathway components seem to relevantly contribute to the control of secretory plasticity, thereby enabling endocrine cells to finely adjust their dynamic response to the specific hormonal requirements.     

Secretory dynamics of bioactive and immunoactive LH during the oestrous cycle of the sheep

Blood samples were collected every 15 min for 6 h during the follicular (1 day before oestrus), and early (Days +1 to +3), mid- (Days +4 to +8), and full (Days +9 to +14) luteal phases of the oestrous cycle. Serum concentrations of immunoactive LH were measured by radioimmunoassay. The biological activity of serum LH was determined by an in-vitro bioassay that uses LH-induced testosterone production from mouse interstitial cells as an endpoint. Only ovine and bovine LH and hCG had appreciable activity in this bioassay. The temporal pattern of secretion of bioactive LH paralleled the secretory pattern of immunoactive LH at all stages of the ovine oestrous cycle. However, the secretory pattern itself varied regularly through the oestrous cycle. The frequency of secretory excursions of LH was highest during the follicular phase (6.2 +/- 0.9 pulses/6 h) and was progressively reduced through the luteal phase (1.1 +/- 0.1 pulses/6 h during full luteal phase). Conversely, amplitude of secretory excursions of immunoactive LH was low during the follicular phase (0.79 +/- 0.08 ng/ml) and significantly (P less than 0.05) increased during the mid- and full luteal phases (1.49 +/- 0.10 and 2.37 +/- 0.20 ng/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in pituitary oxytocin and vasopressin during the estrous cycle and after ovarian hormones: evidence for mediation by norepinephrine

Pituitary levels of oxytocin and vasopressin were maximal on the morning of proestrus, declined during estrus, and were lowest on metestrus in cycling female rats. Norepinephrine levels in the paraventricular nucleus were decreased on proestrus and estrus when compared with metestrus-diestrus. Norepinephrine did not vary in the supraoptic nucleus. Administration of estradiol benzoate to ovariectomized rats elevated oxytocin in the pituitary 54 hr later. This elevation was not affected by a subsequent injection of estrogen or progesterone. Estrogen priming did not affect vasopressin levels in the pituitary, but a second injection of estrogen or of progesterone 48 hr later increased vasopressin in the pituitary when measured 6 hr after the second injection. Vasopressin was decreased 30 hr after a second injection of estrogen. The ovarian hormone treatments that elevated pituitary vasopressin decreased steady state levels of norepinephrine in the paraventricular nucleus and reduced the depletion of norepinephrine after administration of the catecholamine synthesis inhibitor α-methyltyrosine, suggesting a decrease in turnover. Ovarian hormones did not affect norepinephrine in the supraoptic nucleus. The present results suggest a role for posterior pituitary hormones in reproductive processes and a role for noradrenergic mechanisms in the paraventricular nucleus in mediating the effects of ovarian steroids on pituitary vasopressin.     

Molecular and morphological evidence on the phylogeny of the Elephantidae

The African and Asian elephants and the mammoth diverged ca. 4-6 million years ago and their phylogenetic relationship has been controversial. Morphological studies have suggested a mammoth Asian elephant relationship, while molecular studies have produced conflicting results. We obtained cytochrome b sequences of up to 545 base pairs from five mammoths, 14 Asian and eight African elephants. A high degree of polymorphism is detected within species. With a dugong sequence used as the outgroup, parsimony and maximum-likelihood analyses support a mammoth African elephant clade. As the dugong is a very distant outgroup, we employ likelihood analysis to root the tree with a molecular clock, and use bootstrap and Bayesian analyses to quantify the relative support for different topologies. The analyses support the mammoth African elephant relationship, although other trees cannot be rejected. Ancestral polymorphisms may have resulted in gene trees differing from the species phylogeny Examination of morphological data, especially from primitive fossil members, indicates that some supposed synapomorphies between the mammoth and Asian elephant are variable, others convergent or autapomorphous. A mammoth African elephant relationship is not excluded. Our results highlight the need, in both morphological and molecular phylogenetics, for multiple markers and close attention to within-taxon variation and outgroup selection.     

Cytological changes of the pituitary basophils in rats slowly infused with thyrotropin-releasing hormone (TRH).

Young male rats were slowly infused with synthetic TRH, 1 microgram/hr, for 1, 3, 24, 48 and 72 hr, respectively. In the control rats, the basophils of the pituitaries can be divided, in their cytological properties, into the II- (classical thyrotrophs), II/III-,III, (classical LH-cell), and III/IV-type cell. The typical IV-type cells (classical FSH-cell), however, are scarcely found in the young rats. Following 1-hr infusion of TRH, the II-type cells decrease in number with the advancement of granular release, but morphological changes are not yet concrete on the other types of basophils. The II-type cells are quickly invisible following a 3-hr infusion, while the III- and III/IV-type cells remain without any significant changes. The III- and III/IV-type cells are progressively degranulated after a 24-hr infusion. The diameter of secretory granules is reduced to 100--150 nm. The smallest ones below 50 nm in diameter, are disintegrated to disperse into the ground matrix. After degranutlaion, the III/IV-type cells appear to revert to the polygonal or stellate cells with the identical fine structure with the II-type cells. There is evidence that the thyroidectomy cells may develop from the III/IV-type cells only after a 48-hr infusion. After 72 hr, most basophils are provided with the uniform structure of "reversionary II-type cells". In reference to the high serum TSH concentration and no significant change of pituitary TSH concentration under the same experimental condition (Soji, 1978), the present author conclusively postulates that the degranulation of the III/IV-type cells may mainly reflect the conspicuous elevation of serum TSH concentration. The above morphological results are contradictory a plausible view that TRH acts only upon the thyrotrophs to release TSH. The fact that all the basophils ultimately take an appearance of "reversionary II-type cells" in the gland by the prolonged infusion of TRH may not only suggest the share of responsiveness of all the basophils to TRH, but also support the hypothesis of secretory cycle of the basophils.     

Human pituitary thyrotropin. Isolation and characterization of the hormone and its subunits.

Procedures have been described for the isolation of highly purified thyrotropin form frozen or acetone-preserved glands or from side fractions of somatotropin isolation and for the separation of its alpha and beta subunits. The products have been characterized by terminal residue analyses, amino acid composition, carbohydrate content, disc electrophoresis, ultracentrifugation, and biological activity.     

Functional and morphological identification of FSH- and LH-producing cells in the pituitary gland

The identification of pituitary FSH and LH cells in states of pharmacological treatment influencing the pituitary FSH and LH production was performed by histological staining at the isoelectric points of these hormones in the cat. The intensity of the stained material in the hormone-producing cells was determined by a microphotometric technique. As a physiological control, the FSH and LH levels in blood were measured by a radioimmunoassay.     

Secretory activity of lactotrophs and its regulation by hypothalamic hormones in primary cultures of pituitary cells of rats of different ages]

Basal prolactin (PRL) secretion and the responses of lactotrophs to thyroliberin, dopamine and somatostatin were studied in the experiments employing primary monolayer cultures of pituitary cells obtained from developing rats of different ages. High responsiveness of PRL-secreting cells to the action of hypothalamic hormones was observed in the group of neonatal rats, although basal PRL release was about two orders lower in pituitary cultures of neonatal rats as compared to the cultures of immature, pubertal and adult animals. The investigation performed could reveal quantitative, but not qualitative differences in the reactions of lactotrophs of various age groups. It is concluded that postnatal development in the rat is coupled with significant changes of basal PRL release and to a lesser extent, with changes of lactotroph responsiveness to hypothalamic hormones.     

Secretory and absorptive activity of oesophageal epithelium: evidence of circulating mucosubstances

Summary The space between the oesophageal basal and prickle epithelial cells appears empty by standard ultrastructural preparative techniques. Fixation of human oesophageal biopsies with a variety of agents, including tannic acid, glutaraldehyde—lysine, cetylpyridinium chloride and Ruthenium Red shows that this space is filled with mucosubstances, some free, some attached to the cells as a glycocalyx. There is evidence that this material is secreted constitutively by the basal and prickle cells. This secretion may be changed or blocked by incubating oesophageal biopsies in the presence of colchicine or dinitrophenol. Incubation at 16°C has the same effect. Absorption from the intercellular space may be followed using the fluid phase marker, horseradish peroxidase. Early endosomes may also be shown by their acid phosphatase activity. Incubation of biopsies at 20–22°C allows early endosomes to accumulate material, but not pass it on the late endosomes.