Perinatal Activity of the Hypothalamic-Pituitary-Gonadal Axis in the Lamb. I. Circulating Levels of LH, FSH, Prolactin and Testosterone and in vivo Response to hCG in the First Two Months of Life

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Abstract
Plasma LH [luteinizing hormone] and FSH [follicle stimulating hormone] peaks were observed from the 1st wk of life but plasma LH was not consistently followed by an increase in T [testosterone] at 8 wk. Although plasma FSH and PRL [prolactin] fluctuated with no specific trend observable, plasma FSH was higher in female than in male lambs. During a 6 h observation period, fewer spontaneous peaks of LH or T were observed at 4 wk than at 2 or 8 wk of age. A significant in vivo T response to hCG [human chorionic gonadotropin] administration at 2, 4 and 8 wk was observed but the mean T area was greater at 8 wk. These studies indicate an active hypothalamic-pituitary axis in the newborn lamb of both sexes and early testicular activity. However, the steroidogenic testicular responsiveness to endogenous LH appears to be lower at 8 than at 2 wk of life. The existence of an early activation of the pituitary gonadal axis in the immature male lamb would suggest its usefulness as an exerimental model for the study of early postnatal gonadal activity in man.

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