The effect of apomorphine and ergocriptine on the release of MSH by the pars intermedia of Rana pipiens.
In an attempt to further characterize the nature of the innervation controlling melanophore-stimulating hormone (MSH) release from the pars intermedia (PI), pellets containing either apomorphine or ergocriptine were implanted in contact with the PI of the frog, and the effect on the animal's coloration was observed. Frogs with apomorphine implants exhibited skin pallor for several hours and those with ergocriptine implants were pallid for a few days. Hypophysectomized (HX) frogs which had been darkened with MSH regained their pallor no sooner when given an injection of apomorphine than with the vehicle. However, intact dark frogs lightened when injected with apomorphine. Frogs darkened by autotransplantation of the PI to the dorsal lymph sac were lightened by an injection of apomorphine. Frogs lightened by an ergocriptine implant on the PI and then darkened by MSH did not lighten sooner than HX frogs given an injection of MSH. Ergocriptine-containing pellets implanted in the thigh took longer to produce the same effect than those implanted in contact with the PI. Since apomorphine is known to stimulate dopamine receptors in the central nervous system, and there is some evidence that ergocriptine does also, the above evidence supports the hypothesis that dopamine receptors are present in the PI.
D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000494:pharmacology*; D004343:Drug Implants; D004873:Ergolines / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D008547:Melanophores / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D011894:Rana pipiens
D004343:Drug Implants; D004873:Ergolines; D009074:Melanocyte-Stimulating Hormones; D001058:Apomorphine