Effects of prolactin administered to a perfused area of the skin of Angora goats
R. Puchala, S. G. Pierzynowski, T. Wuliji, A. L. Goetsch, S. A. Soto-Navarro, and T. SahluJournal of Animal Science 81:279-284. 2003
Decreased fiber growth by some breeds of sheep and Angora goats in early lactation has been attributed to a regulatory role of prolactin on increased nutrient use by the mammary gland. In addition to indirect influence, direct effects of prolactin on follicles are possible. It has been suggested that the plasma concentration of prolactin in goats and sheep is greater in venous blood of the skin than in systemic venous blood. Although it is widely accepted that the pituitary gland is the major site of prolactin synthesis, molecules with a structure similar to prolactin are synthesized in other tissues, such as the placenta, lymphocytes, and possibly the skin. Published reports of prolactin on fiber growth are contradictory, with some findings suggesting stimulatory, inhibitory, or no effects. However, because research in this area is not extensive, and since many studies of influences of hormones and metabolites on fiber growth also entail changes in metabolism by tissues other than the skin, an experiment was conducted with a skin perfusion technique to investigate the effects of infusing prolactin into a small artery supply blood to a defined area of skin of Angora goats, without influencing conditions in other tissues, on mohair fiber growth. Seven Angora wethers (average body weight of 30 kg) were used, with prolactin infused on one side of the wethers to triple the normal concentration in the perfused region, although the actual realized increase in concentration was approximately twice the normal level. A control, saline solution was infused on the other side not receiving prolactin, thus permitting each wether to serve as its own control. Prolactin decreased mohair fiber growth in the perfused area of skin, implying a direct effect on skin metabolism and fiber growth. The decrease in mohair fiber growth was accompanied by a decrease in mohair staple length, indicating that all or a substantial portion of change in fiber growth was because of actions on active follicles rather than an increased number of inactive follicles. Oxygen saturation of hemoglobin in venous blood draining the perfused region was decreased by prolactin. In addition, concentrations of the amino acids methionine, lysine, valine, isoleucine, and leucine in venous blood on the side infused with prolactin were greater than in blood from the control side. Results of this experiment suggest that effects of prolactin on mohair fiber growth may not be limited to simple competition of nutrients between skin and other tissues such as the mammary gland. Likewise, decreased amino acid and energy use by follicles of Angora goats when prolactin is elevated, such as in late pregnancy and early lactation, may contribute to partitioning of nutrients to other tissues.
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