Differences in the Cardiac and Pressor Responses to Propranolol of Rats and Guinea Pigs

Abstract

Abstract-Propranolol produces a sustained rise in blood pressure in the rat, but little change in the guinea pig. In order to elucidate this distinct difference, the fol lowing experiments were carried out: (a) The pressor effect of propranolol was studied while the vascular tone was changed by infusion of several vasoactive substances in the guinea pig; (b) The effect of propranolol on the isolated atria of rats and guinea pigs was also compared. Propranolol always produced a pressor action during the infusion of adrenergic β-stimulating agents, but not during vasopressin infusion. In spontaneously beating or electrically driven guinea pig atria, propranolol reduced the contractile force to a greater extent than in rat atria. It is concluded that the dif ference in action of propranolol on the blood pressure of rat and guinea pig may be explained by the following two reasons: (a) the β-adrenoceptive vasodilator tone in skeletal muscle is stronger in the rat than in the guinea pig; (b) the heart of the rat is less sensitive to propranolol than that of the guinea pig.Many investigators (1-5) reported that propranolol produced a fall in blood pressure in various species of experimental animals. Hypotensive effects of propranolol have been also reported in patients after prolonged oral administration (6-8). Meanwhile we re ported in previous papers (9, 10) that propranolol produced a sustained pressor action in the rat. This action may be due to the blockade of the ~-adrenoceptive response of peripheral vascular smooth muscle which dominates the maintenance of normotension in the rat.Such diverse pressor action of propranolol in the rat may be explained as follows:(a) The j-adrenoceptive vasodilator activity maintains the tone in blood vessels of skeletal muscle mediated through the central nervous system more effectively in the rat than in the other species of animals, or (b) the heart of the rat is less sensitive to propranolol than that of other species.In this experiment, guinea pigs were compared with rats as to the pressor effects of propranolol when the vascular tone was changed by the infusions of various vasoactive substances. The effects of propranolol in the isolated atria of rats and guinea pigs were also compared. MATERIALS AND METHODS I. Experiments in guinea pigsGuinea pigs of both sexes, weighing between 350 and 450g were anesthetized with urethane (1.5 g/kg s.c.). Arterial blood pressure was measured at the right carotid artery

Effects of Several Beta-Blocking Agents on the Development of Hypertension in Spontaneously Hypertensive Rats

“…Furthermore, ;3-blockers have potential hypertensive effects, since they release catecholamines from the adrenal medulla (15), and can produce in the rat constriction of the artery through blockade of vascular ;3-receptor, for the vascular s-receptors in the rat receive rich tonic influence (32 …”

Role of Beta-Adrenoceptors in Cooling-Evoked Hemodynamic Perturbations of Rats: Investigation by Spectral Analysis

“…We assumed there is a heightened vasodilatation effect after sympathetic tonus is removed by HEX or GUA, thus PRO may raise BP in the condition of higher peripheral vasodilator tonus [20]. Compared with PRO-only, however, HEX+PRO attenuated most spectral powers, particularly with respect to LF BPV , the result indicated that uprising of efferent sympathetic discharges by reducing the afferent input of baroreflex loop is responsible for the PRO effect.…”

“…It is known that rat has a strong β-ADR tone in the peripheral vascular beds [20]. Our present study under PreCS, i.e., a resting condition, showed although PRO-only did not change SBP and HR, it exerts converse effects on BPV and HRV in terms of their spectral powers, they are increased in BPV and decreased for most of the HRV (VLF HRV and LF/HF HRV ), except that HF HRV was increased.…”