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Plasma Prolactin, LH, FSH and Estrogen Excretion Patterns in Gilts during Sexual Development¹

Institut National de la Recherche Agronomique, France

Abstract

Plasma prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay in groups of eight gilts sampled every 20 min for 6 h at about 2-wk intervals between IS and 192 d of age. The PRL levels were high at 15 and 28 d, declined at 40 d just after weaning and then rose slowly until 192 d of age. The number of LH pulses during 6 h was higher between 83 and 125 d than at the other periods. Magnitude of LH pulses was highest at 15 d, constant from 54 to 125 d, fell at 137 d and remained low until 192 d. Plasma FSH was high from 15 to 125 d, with a maximum at 54 d. It declined slowly until 168 d and did not change thereafter. Estrogen excretion was estimated from urine excretion of estrone (E₁; conjugated plus nonconjugated E₁) per 24 h from 40 d until puberty in three gilts and at 156 and 174 d in two other animals. The E₁ excretion increased with age and four levels were described before peak values with the onset of first estrus. The first increase in E₁ excretion occurred between 68 and 110 d, when antral follicles appeared in the ovaries. It was subsequent to the highest levels of FSH and concomitant with the increased frequency of LH pulses. The drop in levels of both gonadotropins after 125 d probably corresponded to the development of the negative feedback as a result of greater ovarian activity in these gilts.

¹ The authors gratefully acknowledge Dr. G. Hennen (Centre Hospitalier Universitaire, Sart Tilman, Belgium) for welcoming one of us in his laboratory to perform the assay of FSH, Dr. J. L. Vandalem (Centre Hospitalier Universitaire, Sart Tilman, Belgium) for technical advice and FSH level calculations, Dr. M. Terqui, (Institut National de la Recherche Agronomique, France) for technical advice and critical evaluation of the manuscript, J. C. Hulin and J. Lebost for technical assistance.

² Station Centrale de Physiologie Animate, 78350 Jouy en Josas, France.

³ Station de Recherches sur l'Elevage des Pores, Centre de Rennes St Gilles, 35590 L'Hermitage, France.

⁴ Station de Physiologie de la Reproduction, Centre de Tours-Nouzilly, 37380 Monnaie, France.

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