The effect of a Subcutaneous Implant of Naxalone on the Pulsatile Secretion of LH in the Prepuberal Goat During Anoestrus

Abstract

From a commercial flock, 15 prepuberal does of the Alpine breed were selected, body weight and age averaged 35.8 kg and 8 months, respectively. The experiment was carried out during the months of May and June when anoestrus is more incipient in this latitude (19°13'N). Feeding and handling was conventional with water ad libitum. In groups of 5 chosen at random, they were treated as follows: Group A was used as control, group B received an implant of 15 mg naloxone. And group C received an i.m. injection of 0.5 mg naloxone i.m. at 12 h intervals for 15 days. To observe the effect of this experimental treatment on the pattern of secretion of LH, on day 0 a blood sample (2 mL) was obtained through a cannulae implanted in the jugular vein every 20 min for 7 h continuous. Blood samples were allowed to coagulate at room temperature and thereafter, centrifuged at 2.500 rpm for 15 min; plasma was decanted into small plastic vials and stored frozen until LH assay was carried out. Blood samples were obtained on day 0, 5, 10, 15 and 20. Plasma concentration of LH was determined by RIA as previously reported. And the statistical analysis of LH concentrations was studied using a descriptive method followed by an inferential screening and a variance analysis. It was observed that the plasmatic concentrations of LH changed through time in all groups, changes were more pronounced in the naloxone treated animals as compared with the control group. It was observed that there was no significance on the interaction between treatment and the sampling day. An influence of time upon the plasmatic levels of LH was observed, showing a high degree of significance (f = 12.58 (4.44) p = 0.0000005). There was tendency of an increase in LH secretion through time observed in all groups. A large difference was detected when comparing plasma LH from the first 2 samples with samples obtained in days 10, 15 and 20 of the experiment. It was observed that the effect of naloxone through time did not show significant differences until after the second week of treatment. This results give further support of the important role that endogenous opioids on the control of reproduction of sheep.