LEPTIN AND PROSTAGLANDIN F RECEPTOR GENE EXPRESSION OF ADIPOCYTES OBTAINED AT ESTRUS AND THE MID-LUTEAL STAGE OF THE ESTROUS CYCLE OF HEIFERS TREATED WITH PROSTAGLANDIN F2α AND 15-KETOPROSTAGLANDIN F2α REVISITED

Abstract

Leptin is a potent satiety hormone synthesized and secreted by adipocytes. It was first documented in morbidly obese infertile mice (ob/ob) in the 1950's; however, the gene was not cloned until 1994. The discovery has lead to various studies in both nutrition and reproduction. The absence of leptin in circulation results in infertility suggesting that leptin may be signaling the brain of the body's energy reserves in the form of fat, which is required for reproductive function. Interestingly, leptin gene expression has been reported to differ relative to stage of the estrous cycle in adipose tissue. In heifers, leptin gene expression is higher in adipose tissue obtained during estrus and the early to mid-luteal stage of the estrous cycle when compared with the late-luteal and the follicular phase when expression was lower. Prostaglandin F2α (PGF2α), which is quickly metabolized to 15-keto-prostaglandin F2α (15-keto-PGF2α), is present during the estrous cycle when the change in leptin gene expression was reported. Therefore, our hypothesis is that leptin gene expression will decrease in adipocytes obtained at estrus and mid-luteal stage of the bovine estrous cycle treated with PGF2α or 15-keto-PGF2α. Subcutaneous adipose tissue (∼6 g) was obtained at estrus and the midluteal stage of the estrous cycle of Brahman influenced heifers (n=10). Approximately 4 g of tissue was digested and cultured with PGF2α and 15-keto-PGF2α at concentrations of 10−11, 10−10, 10−9, 10−8 and 0 M respectively for 18 h. The remaining two grams were immediately snap frozen in liquid nitrogen in order to measure leptin and prostaglandin F receptor (PGFr) gene expression at the time of tissue collection. Prostaglandin F2α has been reported to have the ability to regulate its receptor; therefore, PGFr gene expression was quantitated as a control for treatment of adipocytes. Leptin and PGFr mRNA was quantitated using real time PCR. Values obtained from adipose tissue were transformed to log10 and the values obtained from culture were expressed as a percentage of 0 M (0 M=100%). The effect of treatment, stage and stage X treatment were determined using the MIXED procedure of SAS. The ESTIMATE procedure of SAS was used to determine the differences between treatment dose means. As previously reported leptin production did not differ in adipose tissue collected during the estrus or the mid-luteal stage of the estrous cycle. Similarly, PGFr gene expression did not differ relative to stage in tissue. Neither leptin nor PGFr gene expression was affected by 15-keto-PGF2α in adipocytes. However, PGF2α tended (P≤0.1) to decrease leptin gene expression in adipocytes obtained at estrus at physiological doses (10−8 M 80.5%±12.7%). PGFr gene expression tended (P≤0.1) to increase in adipocytes obtained at estrus at concentrations of 10−11 (162.5%±42.4%), and 10−9 M (165.7%±42.4%) implying that adipocytes were responding to treatment. No effect on leptin gene expression was determined in adipocytes obtained during the mid-luteal stage of the estrous cycle. However, PGF2α tended (P≤0.1) to decrease PGFr gene expression at 10−11 (75.0%±11.4%) dose. Collectively, the data suggests that PGF2α and its primary metabolite may not affect leptin gene expression alone; suggesting a combination of reproductive hormones may be responsible for the differences reported during the estrous cycle. (poster)