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Abstract. The objectives of this research were to characterize plasma profiles of growth hormone (GH), prolactin (PRL) and insulin-like growth factor-I (IGF-I) during gestation and the lactation period in goats, as well as in their suckling growing kids. There were no obvious changes in the GH or PRL profiles during gestation, but secretion of both GH and PRL increased acutely after parturition. The elevated GH concentrations were maintained until 3 months after parturition, whereas the PRL concentrations decreased gradually after parturition. The elevated hormone concentrations are thought to be caused mainly by an increase in the secretory pulse amplitudes. In contrast to the GH and PRL profiles, the plasma IGF-I concentrations during late gestation were significantly higher than the post-parturition concentrations, and the IGF-I concentrations in late gestation decreased gradually until the day of parturition. The plasma GH, PRL and IGF-I concentrations in kids 1 week after birth were high, and concentrations of each hormone decreased thereafter. These results show that the increased secretory potencies of pituitary GH and PRL after parturition are caused mainly by an increase in the secretory pulse amplitudes and that plasma GH is inversely related to plasma IGF-I compared over gestation and the lactation period in goats. Key words: GH, PRL, IGF-I, Gestation, Lactation.(J. Reprod. Dev. 45: [273][274][275][276][277][278][279][280][281] 1999) G estation is a composite of integrated processes, resulting in the successful development of fetuses and the birth of offspring. The energy and nutrient requirements in pregnant animals are increased during gestation [1]. The survival of newborn animals is dependent on an adequate supply of milk secreted from the mammary glands of the mother after parturition [2]. Since growth hormone (GH) regulates many aspects of metabolic activity [3], it is meaningful to examine the GH profiles throughout gestation and during the lactation period in animals. Plasma or serum concentrations of GH and prolactin (PRL) in ruminants have been observed to elevate acutely during the periparturient period [4][5][6][7][8][9]. In these published observations, however, blood samples were usually collected for only a few weeks around parturition, and plasma profiles of GH and PRL have never been examined throughout gestation. Moreover, the blood samples were collected only about once a day, although GH and PRL are known to be secreted in transient pulses [3,[10][11][12][13][14]. PRL is required for the initiation of lactation [15,16]; therefore, it is of interest to determine how the pulsatile secretory patterns of both GH and PRL change throughout gestation and during the lactation period in animals. The anabolic action of GH is

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]bGRF29 at 2-h intervals were examined. bGRF-29 acutely increased plasma GH levels after each injection, and the high GH levels decreased to the basal values within 2 h. In contrast, high GH levels induced by [D-Ala2, A1a15]-hGRF-29 were gradually decreased but not lowered to basal values throughout the experiment. These results show that [D-Ala2, Ala15]bGRF29 has longer-lasting and greater GH-releasing activity than the other GRF analogs in female calves, and the GH-releasing potency of rat GRF is approximately equal to that of bovine GRF in cattle in vivo.

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