Extraction of human chorionic thyrotropin (hCT) from term placentas: failure to recover thyrotropic activity

Pituitary gland and pregnancy

The hypothalamic-pituitary-adrenal axis is central to mammalian reproductive function, including conception, pregnancy maintenance, parturition, and breastfeeding. Pregnancy is associated with substantial physiologic changes within this endocrine axis to meet the demands of pregnancy, which include support of the fetus (volume support, nutritional and oxygen supply, clearance of fetal waste), protection of the fetus (from starvation, drugs, toxins), preparation of the uterus for labor, and protection of the mother from potential cardiovascular injury at delivery. This article reviews the anatomy, embryology, and physiology of the pituitary. The effect of pregnancy on pituitary structure and function, in health and disease, also is discussed.

Extrapituitary beta TSH and GH in early chick embryos

Somatotropes and thyrotropes are thought to be derived from the same cellular lineage and the expression of both growth hormone (GH) and thyrotropin (beta TSH) is thought to be dependent upon the same (Pit-1) transcription factor. The presence and comparative distribution of GH- and beta TSH-immunoreactivity in early chick embryos, was therefore investigated, especially as extrapituitary GH-immunoreactive cells are present in some peripheral tissues of early chick embryos prior to the ontogenic differentiation of the pituitary gland. At the end of the first trimester of incubation (embryonic day (ED) 7), GH-immunoreactivity was widespread in the head, particularly in neural tissue. Strong labeling was found in the diencephalon and mesencephalon and in neural ganglia and the trigeminal nerve. beta TSH-immunoreactivity was also present in these tissues, although restricted to the ependymal cells lining the diocoele and mesocoele and absent from mantle layers. It was also present in the cellular layer lining the otic vesicle, which was devoid of GH staining. In contrast, Rathke's pouch, the primordial pituitary gland was without GH- or beta TSH-staining. Control sections incubated with preabsorbed antisera or with pre-immune serum were completely devoid of staining. In the trunk, the epidermal cells were stained for beta TSH, but not for GH. Intense GH-immunoreactivity was present in the ventral and dorsal horns of the spinal cord and was particularly strong in the outer marginal layer. In contrast, beta TSH-immunoreactivity was again restricted to ependymal cells lining the spinal canal, which were devoid of GH-immunoreactivity. Strong GH staining was also present in the dorsal and ventral root ganglia, both of which lacked significant beta TSH staining. In non-neural tissues, both GH and beta TSH staining was present in the crop, although in topographically different cells. beta TSH-immunoreactivity was also present in the cells lining the bronchial ducts and the adluminal linings of the pleural and pericardial cavities. GH-immunoreactivity, in contrast, was absent from the lung but present in the surrounding intracostal muscles and in the Müllerian duct. Both GH- and beta TSH-immunoreactivity was present in liver hepatocytes. These results clearly show, for the first time, the presence of TSH-immunoreactivity in central and peripheral tissues of the ED7 chick embryo, prior to the differentiation of pituitary thyrotropes. They also show that beta TSH- and GH-immunoreactive cells are differentially located within embryonic tissues.

Thyroid stimulation by placental factors

There is now convincing evidence that the human placenta produces factors which have some role in regulating maternal thyroid function during normal pregnancy and are capable of inducing overt hyperthyroidism in some pregnant women and in patients with trophoblastic tumors. As far as the biochemical nature of these placental thyroid stimulators is concerned, a bulk of evidence indicates that hCG, which is abundant in the blood of pregnant women and patients with trophoblastic diseases and shares some structural similarities with human TSH, is the putative thyroid-stimulating factor. However, it is disturbing that most in vitro studies have failed to prove that hCG is truly capable of stimulating the human thyroid. Therefore, factors other than hCG have also to be considered, particularly some molecular variant forms of hCG with enhanced thyrotropic activity. Both the existence of tumor-associated hCG variants in patients with trophoblastic diseases and their ability to stimulate thyroid hormone release in human thyroid tissue have been demonstrated. To complicate things further, other variants of hCG have been identified and purified from pregnancy urine that have a thyroid inhibitory effect in human thyroid membranes. The variant forms of hCG have been shown to differ from the native hormone mainly in the carbohydrate moiety, with the more acidic, more glycosylated variants being the ones capable of stimulating the human thyroid and the more alkaline sialic acidic deficient variants on the other hand, being potent thyroid inhibitors. Future studies should reveal if the different thyroid stimulators and thyroid inhibitors may possibly interact with specific regions of the human TSH receptor that confer their respective functional activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal serum hormone changes during abortion induced with 9-deoxo-16, 16-dimethyl-9-methylene prostaglandin E2

Serum hormone levels in women undergoing successful first and second trimester abortions induced by 9-deoxo-16, 16-dimethyl-9-methylene prostaglandin E2 vagitories have been measured. Significantly decreased levels of prolactin (p less than 0.01) and TSH (p less than 0.05) were seen in both groups of women but the drop appeared sooner, within two hours, in first trimester abortions. Regardless of gestational length there was a significant decrease in serum human chorionic gonadotropin (hCG) (p less than 0.01) concentrations in maternal serum six hours into treatment. In the second trimester abortions total estriol, alpha-fetoprotein and lactoplacental hormone hPL were analysed in maternal serum but the levels did not change over the eight hour investigation period. It is speculated that the PGE2-derivative most likely affects the maternal pituitary secretion of prolactin and TSH, possibly via direct or indirect interference with TRH mechanism(s).