Anterior pituitary hormones

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Pharmacology and toxicology

The hormones of the anterior lobe of the pituitary gland regulate hormone released by the peripheral hormone glands. The release of anterior pituitary hormones is controlled by the hypothalamic releasing hormones. Because of their high molecular weight, pituitary hormones do not cross the placenta. Therefore, a direct effect on the fetus is not to be expected. The following hormones are released from the anterior pituitary gland.

Growth hormone (GH, somatropin, STH)

This has effects on somatic growth and on metabolism. A hormone similar structurally and functionally to GH is produced in increasing quantities by the placenta in advanced pregnancy. It is referred to as human placental lactogen (HPL) or, less often, as human chorionic somatomammotropin (HCS). Functionally, this hormone is similar to prolactin.

Prolactin is a polypeptide hormone whose main role consists of the stimulation of lactation in the postpartum period. A physiological increase in prolactin secretion occurs during pregnancy and lactation, but also in hypothalamic and pituitary diseases. Prolactin has no therapeutic use.

Follicle stimulating hormone (FSH, urofollitrophin, foilitrophin-tx, follitrophin-fl)

This stimulates growth and maturation of the ovarian follicle, and granulosa cell release of estrogen. Luteinizing hormone (LH) stimulates ovulation. During pregnancy, human chorionic gonadotropin (hCG), which is analogous to LH, is synthesized in the placenta, and is responsible for maintaining the corpus luteuni of pregnancy. FSH and a mixture of FSH and LH have been used therapeutically. Human menopause gonadotrophins (hMG) and hCG are two of these mixtures {analogs arc menotropin and urogonadotropin). These hormones are used for ovulation induction and for additional support of the corpus luteum. Inducing ovulation with gonadotrophins can lead to multiple pregnancies: of these, 5-6% involve triplets (Scialli 1986). Two publications report on a rare complex of multiple malformations and four cases of neuroblastoma in infants below 1 year, born of pregnancies involving exposure to gonadotrophins (Mandel 1994, Litwin 1991). These findings were not confirmed in other studies, nor were other pregnancy risks or abnormalities in early childhood and pubertal development associated with use of these agents for ovulation induction.

Thyroid stimulating hormone (thyrotropin, TSH)

This stimulates the synthesis and release of thyroxine.

Adrenocorticotropic hormone (ACTH, tetracosactid)

This stimulates the synthesis and release of the glucocorticoids and mineralocorticoids in the adrenal cortex.

Melatonin is secreted by the pineal gland. Melatonin secretion is regulated on the basis of photic stimuli; in the absence of photic stimuli (at night), melatonin secretion increases. Melatonin coordi nates biological rhythms. It also stimulates progesterone secretion, inhibits prostaglandin synthesis, and has (experimentally) a tocolytic effect (Ayar 2001). The human fetal suprachiasmatic nucleus expresses melatonin-binding sites, and is therefore likely to be affected by both endogenous and exogenous melatonin, with consequences for the prenatal and postnatal expression and entrainment of circadian rhythms. The relevance of melatonin to the maintenance of pregnancy at the feto-maternal interface has been investigated, and results suggest that melatonin seems to regu late the human placental function in a paracrine/autocrine manner (Iwasaki 2005). There is insufficient experience with the therapeutic use of melatonin (for instance, for prevention of jetlag after intercontinental flights) in pregnancy.

Recommendation. There are no indications for using anterior pituitary hormones during an already existing pregnancy. Inadvertent use is not grounds for pregnancy termination or for invasive diagnostic procedures.

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