The mechanism of hypertension and bradycardia following lesions of the caudal ventrolateral medulla in the rabbit: The role of sympathetic nerves, circulating adrenaline, vasopressin and renin

J. M. Elliott, V. Kapoor, M. Cain, M. J. West, J. P. Chalmers

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Lesions of the ventrolateral medulla of the rabbit, coinciding with the A1 noradrenaline cell bodies (A1 lesions) produced fortyfold increases in the plasma levels of vasopressin and adrenaline, a twofold increase in plasma noradrenaline and a substantial increase in plasma renin activity. These increases accompanied the hypertension and bradycardia that follow A1 lesions. The vasoconstriction and hypertension were completely abolished by phentolamine, an alpha-adrenoceptor antagonist, when it was administered before lesions and were markedly reduced when it was given after lesions. On the other hand, administration of an antagonist to the vasoconstrictor action of vasopressin (d(CH2)5Tyr(Me)AVP) or an angiotensin converting enzyme inhibitor had little effect. Prior removal of the adrenal glands prevented any rise in plasma adrenaline levels but had no effect on the pressure response to subsequent A1 lesions. These results indicate that the vasoconstriction and hypertension were predominantly mediated by alpha-adrenoceptor stimulation, acting mainly through sympathetic vasoconstrictor nerves. The fall in heart rate following A1 lesions was approximately halved by pretreatment either with d(CH2)5Tyr(Me)AVP alone, or by blockade of the vagus and sympathetic with scopolamine and propranolol; it was completely abolished by combined pretreatment with all three agents. The experiments show that vasopressin release makes a evoked by the excitatory effects of iron deposition, as has been observed with hypothalamic lesions (45). The present experiments were designed to clarify the peripheral effector systems producing the cardiovascular changes after A1 lesions, and not the central mechanisms responsible.

Original languageEnglish
Pages (from-to)1059-1082
Number of pages24
JournalClinical and Experimental Hypertension
VolumeA7
Issue number8
DOIs
Publication statusPublished - 1985
Externally publishedYes

Keywords

  • Epinephrine
  • Hypertension
  • Rabbit
  • Renin
  • Sympatheitic nerves
  • Vasopressin

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