Immunocytological study of the chronology of pituitary cytogenesis in the domestic pig (Sus scrofa) with special reference to the functioning of the hypothalamo-pituitary-gonadal axis

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This paper reports an immunofluorescent study of the pituitary in the fetal pig (Sus scrofa). Fifteen antisera were used against most of the hormones present in the pituitary. Five types of hypophysial endocrine cells were observed in the anterior and intermediate lobes. We determined the sequential appearance of these various cell types in the fetus. The first hormones found at 33 days were ACTH, beta-MSH, beta- and gamma-LPH and alpha- and beta-endorphin; alpha-MSH appeared at 40 days and STH at 45 days. The glycoprotein hormones, LH (45 days), TSH (50 days) and FSH (60 days), appeared between 45 and 60 days. The density and staining of the gonadotropes increased up to 80 days, at which time they reached values similar to those of the adult. Prolactin was not found until 80 days. An anti-LHRH antiserum was used to study LHRH neuron differentiation between 30 and 70 days of pregnancy. The first immunoreactive perikaryons were found at 40 days but the immunoreactive fibers did not reach the median eminence until about 60 days. However, we observed differentiated capillary loops in the palisade layer of the median eminence only in the 70-day fetus. These results when compared with actual data on the differentiation of the reproductive function in the pig fetus permitted us to define an overall pattern of the differentiation and functioning of the fetal neuroendocrine hypothalamo-pituitary-gonadal system in the porcine species. This pattern includes, (i) autodifferentiation and autofunctioning of the gonads and (ii) autodifferentiation of the pituitary with (iii) later assumption by the hypothalamus followed by a phase during which the whole reproductive system functions.