The effects of central administration of omega-conotoxin GVIA on cardiovascular parameters and autonomic reflexes in conscious rabbits.
1. The effects of central administration of omega-conotoxin GVIA (omega-CTX), an N-type calcium channel blocker, were examined in conscious rabbits implanted with lateral intracerebroventricular (i.c.v.) cannulae. 2. Experiments were performed over 4 consecutive days. On day 1, the baroreceptor heart rate (induced by glyceryl trinitrate and phenylephrine) and Bezold-Jarisch like (elicited by serotonin) reflexes were measured before (0 h) and 2 h after central administration of omega-CTX (3 or 30 pmol/kg, i.c.v.) or vehicle. On days 2-4, resting parameters and reflexes were again monitored but no further omega-CTX was administered. 3. No change in heart rate (HR) was observed in any rabbit treatment group during the experimental period. In the vehicle (n = 6) and omega-CTX 3 pmol/kg (n = 6) groups, small falls in mean arterial pressure (MAP) of 6 +/- 2 and 10 +/- 3 mmHg, respectively, occurred between 0 and 24 h; MAP then remained stable. Baroreceptor-heart rate reflex curve parameters did not change in either of these groups during the 4 day period. 4. Following administration of omega-CTX 30 pmol/kg (n = 7), MAP decreased progressively and by 48 h had fallen by 19 +/- 4 mmHg. Also at 48 h, a 20% decrease in HR range of the baroreceptor-heart rate reflex curve was seen without any change in the lower HR plateau from the 0 h control. This indicates that there was an attenuation of the sympathetically mediated upper component of the curve while the vagally mediated component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)
Whorlow
S L
SL
Department of Pharmacology, University of Melbourne, Victoria, Australia.
Angus
J A
JA
Wright
C E
CE
D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects*; D017704:Baroreflex / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D020916:Conotoxins; D006339:Heart Rate / Q000187:drug effects*; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D010456:Peptides, Cyclic / Q000134:cerebrospinal fluid / Q000494:pharmacology*; D011817:Rabbits; D012018:Reflex / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology
D020916:Conotoxins; D010456:Peptides, Cyclic; D012701:Serotonin; C055407:conotoxin GV