The acute cardiovascular effects of PY 108-068 and PN 200-110 were studied by means of a computerized analysis of the intra-aortic blood pressure (BP) recorded continuously for 26 h in conscious unrestrained spontaneously hypertensive rats. Both compounds were studied at three doses (50, 100 and 200 micrograms kg-1) and each dose was administered intravenously 5 times (09 h 00 min, 14 h 00 min, 19 h 00 min, 24 h 00 min and 09 h 00 min). Baroreflex sensitivity was measured 1 h following the last injection. 2. The two compounds were found to induce rapid (3 min) and dose-dependent falls in BP. After the first administration, these decreases reached -20% and -35% for systolic BP (SBP) and diastolic BP (DBP) respectively with PY 108-068 (200 micrograms kg-1) and -25% and -45% for SBP and DBP respectively with PN 200-110 (200 micrograms kg-1). 3. The duration of the reduction in BP increased with the dose and was much longer for PN 200-110 (180 min for SBP) than for PY 108-068 (20 min for SBP). 4. A tachycardia was associated with the decrease in BP which did not differ at 200 micrograms kg-1 between PY 108-068 (+ 108 beats min-1) and PN 200-110 (+ 103 beats min-1). Baroreflex sensitivity was not significantly increased by either drug. 5. The 5 repeated injections of PY 108-068 and PN 200-110 evoked similar responses. 6. In conclusion, both compounds exhibited marked hypotensive properties. PN 200-110 appeared to be more suitable for further development since its effects were found to be greater and much longer lasting than those of PY 108-068.
