Nerve growth factor: its role in male fertility as an ovulation inducer

Abstract

The studies presented in this thesis were designed to elucidate whether the abundance of ovulation-inducing factor/nerve growth factor (OIF/NGF) in alpaca semen can be used as a biomarker to predict male fertility. The neurotrophin, OIF/NGF has been identified in camelid, cattle and human semen. It is only in camelids, however, that an ovulation-inducing role for OIF/NGF has been described. The information gathered from several studies clearly demonstrate that this protein is the stimulus responsible for initiating the ovulatory cascade in camelids. In addition, intramuscular administration of OIF/NGF resulted in a dose-dependent response in terms of ovulation rate, corpus luteum (CL) lifespan, luteinizing hormone (LH) and progesterone secretion. I hypothesized that the quantity of OIF/NGF differs among male alpacas and this abundance arbitrates ovulation and pregnancy rates as well as CL formation and function. To substantiate this hypothesis, the following questions were answered: 1) can OIF/NGF in alpaca semen be quantified using a radioimmunoassay; 2) does the concentration and total abundance of OIF/NGF in alpaca semen vary within and among male ejaculates; 3) what is the glandular source of OIF/NGF that contributes to the male ejaculate; 4) is OIF/NGF concentration or abundance related to parameters associated with male fertility; 5) can OIF/NGF concentration or total abundance in the ejaculate discriminate fertile and subfertile males using both retrospective and prospective approaches; and 6) can power Doppler ultrasonography be used to assess the luteotrophic effect of OIF/NGF in tissue vasculature of the developing CL? I discovered that the source and the amount of OIF/NGF varies among species. In llamas, OIF/NGF is produced by both the corpus and disseminate portions of the prostate gland. In rats, OIF/NGF was detected in testis interstitial cells and in the lumen of the coagulating gland (anterior prostate). Ovulation-inducing factor/NGF secretion by the ampullae and vesicular glands contributed to its presence in bull (cattle and bison) ejaculates. In elk and white tail deer, OIF/NGF was detected in the ampullae and prostate glands, respectively. To gain an understanding of the abundance of OIF/NGF in ejaculates and changes in its concentration within and among males, OIF/NGF levels in semen were quantified using the radioimmunoassay. The assay developed exhibited parallel displacement curves among recombinant NGF, OIF/NGF purified from llama seminal plasma, llama and bull (cattle) seminal plasma. Ovulation-inducing factor/NGF comprised a greater percentage of the total protein found in camelid ejaculates than in cattle. Ovulation-inducing factor/NGF concentration correlated positively with sperm concentration and negatively with pH and semen volume, while total abundance of OIF/NGF was related to total prostate area and OIF/NGF concentration. Although a correlation was found between sperm concentration, neither OIF/NGF concentration nor total abundance was associated with higher ovulation, pregnancy or live birth rates. A clear association of the quantity of OIF/NGF in the male ejaculate at breeding and CL form and function was not evident. The measurement of CL vasculature by power Doppler ultrasonography, however, was able to determine nonpregnancy in alpacas earlier than the assessment of changes in CL diameter. In summary, my results did not support the hypothesis that the measurement of OIF/NGF concentration or total abundance in alpaca semen can be used to predict fertility in male alpacas.