摘要:

The calcium channel blocker, verapamil (0.1–1.0 mg/kg, i.v.) was administered to anesthetized rats to determine its effects on ventilation and on ventilatory responses to hypoxia and CO2. Verapamil produced a dose-dependent increase in tidal volume (VT) and a decrease in respiration rate (f). The bradypnea due to verapamil was characterized by an increase in expiratory duration (TE) and no change of inspiratory duration (TI). Verapamil produced similar changes inVTandfin vagotomized rats. The increase in respiration rate and minute volume due to hypoxia were inhibited by verapamil (0.5 and 1.0 mg/kg) but the increase in tidal volume due to hypoxia was depressed only with the 1.0 mg/kg dose. On the other hand, the increase inVTdue to breathing CO2was not changed by verapamil (0.1–1.0 mg/kg), but depression of the respiratory frequency response to CO2occurred with 1.0 mg/kg of verapamil. These results indicate that verapamil produced slow, deep breathing and these responses were not mediated by vagal mechanisms. Ventilatory responses to hypoxia were depressed by verapamil. However, since the calcium blocker demonstrated no effect on theVT-CO2relationship, verapamil did not change ventilatory chemosensitivity to CO2. The data also suggest that mechanisms governing the control of respiratory frequency are more sensitive to verapamil than tidal volume responses.

ISSN:0008-4212    

DOI:10.1139/y85-265

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Electrical stimulation of afferent vagal fibres evoked a pressor response in rats after transection of the spinal cord. The pressor response was accounted for by an increased release of vasopressin because it was abolished by the intravenous injection of a vasopressin antagonist. Bilateral electrolytic lesions at the sites of the caudal ventrolateral medulla markedly reduced the pressor response to afferent vagal stimulation but not that to carotid occlusion. It is concluded that the area of the caudal ventrolateral medulla is involved in mediation of the vasopressin-induced pressor response to afferent vagal stimulation.

ISSN:0008-4212    

DOI:10.1139/y85-266

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Tissue extracts of rat heart atria contain a family of peptides with natriuretic and vasorelaxant properties. It has been shown by others that inactivation of this atrial natriuretic factor may involve endogenous peptidases. The present experiments demonstrate that incubation in blood in vitro reduces the natriuretic activity of the factor. Specifically, inactivation was associated with a white cell/platelet fraction, indicating that these blood elements may play a physiological role in the metabolism of this new putative hormone.

ISSN:0008-4212    

DOI:10.1139/y85-267

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Tension responses to ramp shortening of varying speed in whole muscle or single fibres from the plateau of an isometric tetanus, revealed at least two distinct phases. There was a fast initial drop in tension followed by a change of slope and a definite inflexion on the tension record. As the velocity of the imposed length change was increased, the inflexion point appeared at a lower tension. Similar inflexions were not observed during ramp releases to an elastic band or a segment of semitendinosus tendon. The tension records obtained with moderately fast ramp length changes to contracting muscle reflect the T1and T2phases of the tension transients.

ISSN:0008-4212    

DOI:10.1139/y85-268

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

We have studied the effects of milrinone on various cardiac preparations obtained from 6-week streptozotocin diabetic rats. The basal rate of spontaneously beating right atrium from diabetics was significantly lower as compared with controls. Milrinone (5 × 10−5to 8 × 10−4 M) produced a dose-dependent positive inotropic and positive chronotropic effect in left atrium and right atrium, respectively. The positive chronotropic response to milrinone was slightly increased in right atria from diabetic animals. In papillary muscle neither the maximum response nor the pD2value of milrinone was altered significantly in diabetic animals. The pD2values of milrinone in right atrium and left atrium were found to be significantly higher in diabetic preparations compared with controls. The data indicate that the responses to milrinone are either unchanged or enhanced in hearts from diabetic animals.

ISSN:0008-4212    

DOI:10.1139/y85-269

出版商:NRC Research Press    

年代:1985

数据来源: NRC