Lymphocytic Nitric Oxide Secretion during Different Reproductive Phases in Cattle

Nitric oxide (NO) is a biological mediator involved in regulation of various physiological processes including reproduction. NO is produced by many different cells of the body including lymphocytes. In this study, the lymphocytic NO secretion was studied in cattle during different phases of reproduction. Blood samples were collected from Holstein Friesian cows during different stages of estrous cycle like follicular phase and luteal phase and also during various stages of pregnancy like early-pregnancy (d 61-83), mid-pregnancy (d 100-168) and late-pregnancy (d 239-246). Six animals at age of 3-7 years were used in each group. Lymphocytes were separated by density gradient centrifugation technique, and cultured for 72 hours. Then culture supernatant was used for measurement of NO by colourimetric assay based on the Griess reaction. Plasma levels of estradiol and progesterone were also measured by enzyme-immuno assay (EIA) to ascertain the stage of estrous cycle. Lymphocytic NO secretion during mid pregnancy (d 100-168) (35.36± 1.18 μM nitrite) was significantly higher than follicular phase (26.60± 3.71 μM nitrite, P< 0.01); early pregnancy (d 61-83) (28.22± 1.39 μM nitrite, P< 0.01) and late pregnancy (d 239-246) (26.07± 3.25 μM nitrite, P< 0.01). During follicular phase the average estradiol level was 12.65± 2.53 pg/ml. It was significantly reduced to 1.88± 0.47 pg/ml during luteal phase. Plasma progesterone level during luteal phase was 5.09± 0.37 ng/ml. The concentrations of plasma estradiol during follicular phase of estrous cycle were significantly negatively correlated (r = –0.966; P < 0.05) with lymphocytic nitric oxide secretion. So, high level of lymphocytic NO during mid-pregnancy might be regulated by the cirlulating level of the sex steroids. In conclusion, the higher level of lymphocytic NO secretion during mid-pregnancy indicates the role of lymphocytic NO in the maintenance of the pregnancy in cattle, which possibly may be in an autocrine or paracrine manner.