[Changes in the potentiation effect of [D-Ala2, Met5]-enkephalin on pressor responses to l-adrenaline in adrenal-enucleated rats].
Physiological significance of colocalization of enkephalin and adrenaline in the adrenal medulla was studied by examining pressor responses to concomitant administration of [D-Ala2, Met5]-enkephalin (100 micrograms/kg, s.c.) and l-adrenaline (50 micrograms/kg, s.c.) in adrenalenucleated rats. The adrenal medulla of Wistar-Imamichi rats was removed at 3 weeks (3WAdMx) or 12 weeks (12WAdMx) of age. Control rats were sham-operated. Blood pressure (BP) was measured by the tail-cuff method. 1) A single s.c. injection of enkephalin induced a marked rise in BP at 10 min in control male and female and the 3WAdMx-male rats, whereas the 3WAdMx females showed only a 5 mmHg increase at its maximum in the BP following enkephalin administration. 2) In the control male and female rats, the 5 min pretreatment with enkephalin enhanced the pressor response to l-adrenaline, and the pressor effect of enkephalin plus l-adrenaline was suppressed by pretreatment with naloxone (2.5 mg/kg, s.c.). On the other hand, in the 3WAdMx male and female rats, the pressor effect of l-adrenaline was almost completely suppressed by pretreatment with enkephalin. Moreover, pretreatment with naloxone resulted in an increase in BP after administration of enkephalin plus l-adrenaline in the 3WAdMx female rats. 3) In contrast to the control female rats, the pressor effect of enkephalin plus adrenaline was also enhanced by pretreatment with naloxone in the 12WAdMx female rats. The results suggest that the lack from immature age of catecholamine and enkephalin which originate from the adrenal medulla appears to alter the responsiveness of the BP regulatory system to exogenous catecholamine and enkephalin in the rat.
Izumi
M
M
Department of Pharmacology, Teikyo University School of Medicine, Tokyo, Japan.
D000313:Adrenal Medulla / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004357:Drug Synergism; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D004837:Epinephrine