Hypophyseal Pars Tuberalis Research Articles

Photoperiod-dependent changes in TSH-like immunoreactivity of cells in the hypophysial pars tuberalis of the Djungarian hamster, Phodopus sungorus.

Certain secretory cells in the hypophysial pars tuberalis of the Djungarian hamster display marked circannual structural alterations. The present investigation deals with the immunohistochemical properties of this cell group. A distinct TSH-like immunoreactivity was found in secretory cells of this type in the pars tuberalis of animals exposed to long photoperiods, whereas under short photoperiods the TSH-like immunoreactivity was nearly absent. In the pars distalis, the number and distribution of TSH-positive cells did not differ significantly between animals maintained under long and under short photoperiods. LH- and FSH-positive cells could not be detected in the pars tuberalis, but they are clearly present in the pars distalis of both groups of hamsters. Our immunocytochemical results suggest that photoperiodic stimuli influence the secretory activity of TSH-like immunoreactive cells in the pars tuberalis. A connection with the neuroendrocrine-thyroid axis is discussed.

The mammalian hypophysial pars tuberalis: A comparative immunocytochemical study

Despite its occurrence in most vertebrate species, the funciton of the hypophysial pars tuberalis (PT) remains obscure. Recent immunocytochemical studies have demonstrated the presence of hormone-containing cells in the PT of the few species studied. In the present study the secretory cell composition of the PT was characterized in a variety of mammals using immunocytochemistry. Species studied were the mouse, rat, guinea pig, rabbit, sheep, rhesus monkey, baboon, and human. Antisera were chosen on the basis of their ability to identify a distinct cell population in the pars distalis. A total of 21 antisera were used to identify GH, PRL, ACTH, β-endorphin, LH, FSH, and TSH. Gonadotropes were identified in the PT of all eight species and were the predominant immunoreactive cell type in the human, baboon, rhesus monkey, sheep, guinea pig, rabbit, and mouse. Thyrotropes were detected in all species except the sheep. They were the predominant cell type in the rat but were less common than gonadotropes in other species. No other secretory cell types were found, with the exception of occasional somatotropes and mammotropes in some human specimens, and small clusters of opiocorticotropes in the guinea pig. Thus the general pattern in the mammalian PT is the presence of gonadotropes and thyrotropes and the absence of other pituitary cell types. In the human, baboon, and rat, all PT parenchymal cells can be identified immunocytochemically. However, in the rhesus monkey, sheep, guinea pig, rabbit, and mouse, the majority of PT cells do not react with any antisera, and thus their function is unknown. Follicles are common in the PT of most mammalian species, however, the luminal contents do not react with antisera to adenohypophysial hormones.

Influence of photoperiod on the ultrastructure of the hypophysial pars tuberalis of the Djungarian hamster, Phodopus sungorus.

Conspicuous cytological differences are found between specific secretory cells of the hypophysial pars tuberalis of Djungarian hamsters exposed to long and short photoperiods. The cells differ with respect to the shapes of perikarya and nuclei and show diverse amounts of secretory granules, lysosome-like bodies and glycogen.

Hormone Production in the Hypophysial Pars Tuberalis of Intact and Hypophysectomized Rats*

The endocrine function of the hypophysial pars tuberalis is currently unknown. Recent immunocytochemical and electron microscopic studies have shown the presence of gonadotropin-producing cells in this tissue in intact rats. Because the pars tuberalis is not destroyed by hypophysectomy, the objective of the present study was to determine whether this gland is activated to produce pituitary hormones following hypophysectomy. Hormone-producing cells were identified by the unlabeled antibody peroxidase-antiperoxidase method of immunocytochemistry using primary antisera generated against the following hormones: LH, FSH, TSH, GH, PRL, ACTH, and beta-endorphin. In intact control rats, the only cell types detected in the pars tuberalis were gonadotropes and thyrotropes. Most gonadotropes contained both LH and FSH. The TSH cells were a separate cell population, and constituted the majority of pars tuberalis parenchymal cells. As early as 1 week after hypophysectomy, a hyperplastic and hypertrophic response was noted in the gonadotropes, and both cell types showed cytological features characteristic of enhanced hormonal synthesis and secretion. These responses increased with time post hypophysectomy. Secretory cell types not present in the pars tuberalis before hypophysectomy, i.e. somatotropes, mammotropes, opiocorticotrophes, were not activated or induced to differentiate after hypophysectomy. Based on these immunocytochemical observations, the hypophysectomized rat cannot be viewed as an animal totally devoid of anterior pituitary hormones. It has the capacity, or at least the potential, for secretion of LH, FSH, and TSH.

The occurrence of pigment in the pars intermedia and pars tuberalis of the hypophysis, and in the hypophyseal leptomeninges of the rat (domestic and wild)

The occurrence of pigment in the pars intermedia and pars tuberalis of the hypophysis, and in the hypophyseal leptomeninges of the rat (domestic and wild)

Effect of Extracts of Pars Tuberalis of Hypophysis on Urine Secretion.

Saline suspensions or boiled acidulated extracts of the bovine pars tuberalis when injected intravenously into rabbits under paraldehyde anesthesia produce a diuresis differing from that produced by injection of posterior lobe extracts. The resulting diuresis comes on without a marked rise of blood pressure and without the latent period of 3 to 5 minutes (during which the flow of urine is entirely suppressed) which are characteristic accompaniments of posterior lobe diuresis. Diabetes insipidus is held, to be due to injury of the base of the brain in the region of the tuber cinereum. Critical examination of the figures of Bailey and Bremer, and of Curtis, shows that in practically every instance the injury has involved the pars tuberalis of the hypophysis. Bourquin has shown that experimental diabetes insipidus in dogs is an irritation rather than a deficiency phenomenon. Slight cauterization of the floor of the third ventricle produces the diabetes but deeper cautery destroys it. She further concludes that “the diuresis must be due to a substance produced at the site of the causative disturbance” for the diabetes insipidus “runs its typical course after trans-section of the spinal cord at the level of the eighth cervical vertebra, double vagotomy below the diaphragm, and paralysis of the parasympathetic nervous system with atropin.” If the cause of experimental diabetes insipidus is to be ascribed to the irritative production of a hormone in the floor of the third ventricle, it is no less reasonable to suppose that the hormone is derived from the pars tuberah, which is distinctly a glandular structure, than that it is produced by brain tissue.