Maternal--Fetal Endocrine Interrelations: Demonstration of TSH Release from the Fetal Hypophysis in Pregnant Rats Administered Synthetic TRH

Abstract

Intensive physiologic ( 1, 2) and chemical (3, 4) researches during the last decade have recently culminated in the demonstration that the thyrotropin releasing hormone ( T R H ) of the hypothalamus in pigs, cattle, and sheep is a tripeptide, consisting of three amino acids, glu tamic aci d-hi s ti dine-proline (5-7) in that sequence. Bowers and associates (8) have shown further that Sprague Dawley rats (Charles River Breeding Laboratories, Wilmington, Mass.) were maintained in separate cages under controlled conditions of temperature (23 * 1') andartificial illumination ( 7 a.m. to 7 p.m.). Tap water and Purina Rat Chow were allowed ad libitum. On day 20 (a.m.) of gestation, each pregnant rat was injected ip with 8 pCi of I3'I to label iodothyronines in maternal and fetal thyroids. On the next day, pregnant rats were administered subcutaneously 2 50-500 pg of TRH,2 dissolved in 1 ml of saline, every 2 hr until spontaneous delivery occurred. Rats which had not delivered by 3 p.m. (after 3 injections) were subjected to cesarean section. Control pregnant rats received saline injections alone. Thyroidal radioiodine uptakes were determined in mothers and newborn 1-2 hr after the last injection of T R H and 24-28 hr after the labeling dose was administered. The thyroids were homogenized in vials containing 2 % NaOH and radioactivity was determined in a well-type scintillation counter. Blood from neonates was collected by decapitation and thoracic incision several minutes after a heparin injection (0.05 ml). Blood was obtained from mothers under light ether anesthesia by direct cardiac puncture. Radioactivity of the whole blood (0.2-ml samples) was measured immediately after collection. The thyroid and pituitary glands were removed from mothers and newborn (under 2The synthetic TRH was prepared by Dr. Karl Folkers.

The Neuroendocrine Regulation and Function of Growth Hormone and Prolactin in the Mammalian Fetus*

“…However, maternal administration of TRF induced a rise in fetal TSH concentration, suggesting that TRF receptors are differentiated in the fetal pituitary by day 20 of gestation and that TRF passes the rodent placental barrier (151,152). The 5-day-old infant rat has a lower PRL response to TRF than does the adult rat (153).…”

Developmental Changes in Brain TRH and in Plasma and Pituitary TSH and Prolactin Levels in the Rat

“…The administration of TRH is followed by a stimulation of both TSH and prolactin secretion in several species; however, TRH has no effect on prolactin secretion in the rat under normal conditions (4). TRH has been shown to affect the synthesis and release of TSH in the rat during the fetal and neonatal period (5). Although there have been reports on the hypothalamic content of bioactive and immunoreactive TRH (6,7) during the postnatal development, no information is yet available on the evolution pattern of TRH in rat fetuses and on the evolution of TRH in the extrahypo thalamic regions of the brain during the neo natal period.…”

Transfer of TRH through the Placenta and Metabolism in the Fetus of the Guinea‐Pig

“…In the rat, however, D'Angelo, Wall and Bowers (1971) have shown that the fetal adenohypophysis is able to release TSH in response to large amounts (250-500 p g ) of T R H given S.C. to the mother during the perinatal period. Kajihara et al (1972) have found raised colloid droplet formation in the rat fetal thyroid after administration of synthetic T R H i.v.…”