Beta-endorphin may be a mediator of apnea induced by the laryngeal chemoreflex in piglets.
To determine whether beta-endorphin is involved in the laryngeal chemoreflex, we initially injected 0.01-1 mg of beta-endorphin into the cisterna magna (i.c.m.) and registered the respiratory and cardiovascular patterns in 5-10-d-old piglets. From 0.1 to 1 mg of beta-endorphin i.c.m. induced a decrease in the minute volume, heart rate, and blood pressure within 15 min. Within the next 30 min respiratory pauses accompanied by blood pressure increases and reductions in heart rate developed, similar to the respiratory and cardiovascular pattern of the induced laryngeal chemoreflex. Based on these initial data, we decided to induce a laryngeal chemoreflex in piglets pretreated with 0.1 mg of beta-endorphin i.c.m (n = 6), 0.2 mg of beta-endorphin i.c.m. (n = 6), 0.1 mg of beta-endorphin i.c.m. and 100 micrograms/kg naloxone i.v. (n = 6), 100 micrograms/kg naloxone i.v. (n = 6), or water i.c.m. (n = 6). Because elevated levels of hypoxanthine in the vitreous humor may indicate hypoxia before death, we therefore measured the postmortem hypoxanthine levels in the vitreous humor. The laryngeal chemoreflex-induced apnea was shortened in the piglet group pretreated with water i.c.m and naloxone i.v. (p < 0.01) and in the piglet group pretreated with 0.1 mg of beta-endorphin i.c.m and naloxone i.v. (p < 0.05), but not significantly prolonged in the piglet groups pretreated with 0.1 or 0.2 mg of beta-endorphin i.c.m. when compared with the piglets pretreated with water i.c.m.(ABSTRACT TRUNCATED AT 250 WORDS)
D000375:Aging / Q000502:physiology; D000818:Animals; D001049:Apnea / Q000139:chemically induced*; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight / Q000187:drug effects; D002946:Cisterna Magna; D005260:Female; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D019271:Hypoxanthine; D007042:Hypoxanthines / Q000378:metabolism; D007267:Injections; D007830:Larynx / Q000187:drug effects*; D008297:Male; D010865:Pilot Projects; D012018:Reflex / Q000187:drug effects*; D013552:Swine; D014822:Vitreous Body / Q000378:metabolism; D001615:beta-Endorphin / Q000494:pharmacology*
D001786:Blood Glucose; D006454:Hemoglobins; D007042:Hypoxanthines; D019271:Hypoxanthine; D001615:beta-Endorphin