Immune-endocrine interaction in regulation of reproduction in bovines
Abstract
The study on the secretion of lymphocytic growth hormone (GH) and nitric oxide (NO) during various stages of estrous cycle and pregnancy, and in different age groups in cattle was carried out. In this study the effects of leptin, N-nitro-L-arginine methyl ester (L-NAME), sodium nitroprusside (SNP), steroids (estradiol, progesterone and tstosterone), cytokines leukaemia inhibitory factor (LIF) and interleukin-10 (IL-10) and incubation of lymphocytes at different temperatures 37.2°C (hypothermia), 38.6°C (normal cow temperature), 41.0°C (hyperthermia) on lymphocytic GH and NO secretion were studied. Total lymphocytic RNAs in cyclic and pregnant cows were also measured.
The lymphocytic GH secretion was highest during luteal phase and lowest during mid-pregnancy. During mid-pregnancy lymphocytic NO secretion was higher than other stages of pregnancy and estrous cycle. There was no effect of incubation of lymphocytes without any treatment at different temperatures on lymphocytic GH and NO secretion during pregnancy. But incubation of lymphocytes treated with leptin in hypothermic condition decresed lymphocytic GH secretion without affecting lymphocytic NO secretion. There was no effect of steroids (estradiol, progesterone and testosterone) on lymphocytic GH and NO secretion during estrous cycle in cattle. In pregnant cows and in 6 months old calves incubation of lymphocytes with SNP significantly decresed the NO secretion. SNP treatment significantly increased lymphocytic GH secretion only in cyclic non-pregnant cows. Incubation of lymphocytes with LIF and IL-10 increased lymphocytic GH secretion during pregnancy, without affecting lymphocytic NO secretion. Lymphocytic GH secretion was higher in young (2 weeks old) and growing (6 months old) calves than adult cyclic cow. Plasma GH levels were higher during luteal phase in cow than other stages of estrous cycle and pregnancy. Plasma GH levels in young and growing calves were higher than adut cyclic cows. Total lymphocytic RNAs were more in pregnant than cyclic non-pregnant cows.
In conclusion, the lowest level of lymphocytic GH in cattle is at a time when lymphocyric ACTH is very high (previously published work), suggesting a negative correlation among lymphocytic GH and ACTH secretion. Threrefore lymphocytes provide a fine control on immuno-stimulatory and immuno-inhibitory factors during pregnancy. The lymphocytic GH and NO secretion is independent of disease condition involving high fever. But the action of leptin on lymphocytic GH secretion is sensitive to decrease in temperature without affecting the lymphocytic NO secretion. The decrease in NO secretion with SNP treatment in pregnant cows and in 6 months old calves indicates that the control mechanisms for GH secretion is different in cow from pig where SNP treatment results in an elevation of NO levels.The increase in lymphocytic GH secretion with LIF and IL-10 treatments indicates the involvement of cytokines in immunomodulation during pregnancy independent of NO dependent mechanism. Higher lymphocytic GH levels in young and growing calves than adult cyclic animals indicates a possible age dependent role before puberty. Higher lymphocytic RNAs in pregnant cows than cyclic non-pregnant cows indicate changes at molecular level in immunomodulation during pregnancy.