Induction of Luteinizing Hormone Release by Electrochemical Stimulation of the Medial Preoptic Area in Δ ⁹-Tetrahydrocannabinol-Blocked Proestrous Rats

Abstract

The predominant psychoactive constituent of marijuana, Δ⁹-tetrahydrocannabinol (THC), blocks the preovulatory luteinizing hormone (LH) surge and ovulation in rats treated with THC (10 mg/kg body weight) during the early afternoon of proestrus. When THC-blocked proestrous rats were subjected to unilateral electrochemical stimulation (100 µA anodal DC for 45 s) in the medial preoptic area (mPOA), serum LH was significantly elevated at 30, 60 and 90 min after stimulation in comparison with LH levels measured in sham-stimulated control animals at those times. The induced LH release was sufficient to elicit ovulatory responses comparable to the spontaneous ovulations observed in control rats treated only with the drug vehicle. These results are consistent with the hypothesis that THC inhibits gonadotropin secretion by action within the central nervous system, but demonstrate that the central inhibitory effect of THC does not prevent the release of LH-releasing hormone (LHRH) when the LHRH neurosecretory units are activated by brain stimulation. Thus, the antiovulatory effect of THC appears to result from.an inhibition of LH secretion which does not involve the direct blockade of LHRH release.