Role of the dopaminergic system in luteinizing hormone release and ovulation in the hen.
Two experiments were conducted to examine further the role of the dopaminergic system in the ovulatory cycle of the hen. In experiment 1, dopamine (DA; 8 microgram) was injected intraventricularly 14 hr prior to the C1 ovulation (to determine the efficacy of DA in causing premature ovulation) and the DA-receptor blocker, pimozide, implanted intraventricularly for the previous 24 hr was used to assess the specificity of the response. The luteinizing hormone (LH) radioimmunoassays from serial blood samples subsequent to the injection, indicated no effect of the DA treatment on either the time or the magnitude of the preovulatory LH surge. In Experiment 2, an intraventricular injection of DA (10 microgram) was made 8 hr prior to the C1 ovulation (to examine the effect of DA on the normal preovulatory LH surgery) and assay results from blood samples at short intervals immediately after the injection showed no effect of the treatment on plasma LH levels. These results, in addition to the finding that the pimozide implant caused no disruption of the ovulatory cycle, suggest that the dopaminergic system is not essential to the ovulatory process in the hen.