Influnece of age and hypertension on arterial barorecptor reflex activity in male rabbits

الملخص EN

This study aims to evaluate the respective changes in arterial baroreflex function (changes in heart rate and respiratory rate in response to induced increase in blood pressure) in adult, middle aged and old male rabbits, as well as to assess the effect of aging on baroreflex sensitivity and baroreflex regulation of parasympathetic and sympathetic out flow.

In addition, the baroreflex sensitivity was also studied in adult male rabbits rendered hypertensive.

This study included 60 male Baiadi rabbits (10 groups 6 animals each) and four experiments.

Experiment I to evaluate the respective changes in heart rate(HR) and respiratory rate (RR) in response to acute changes in arterial blood pressure (BP) achieved with phenylephrine in adult, middle aged and old rabbits.

Experiment II to study the parasympathetic (vagus) and sympathetic (sciatic) nerve activities (VNA, SNA) in the three different age groups before and during acute blood pressure changes achieved with phenylephrine injection.

Experiment III to evaluate the effect of aging on baroreflex sensitivity as well as the extent to which the parasympathetic and sympathetic nerves were responsible for baroreceptor sensitivity that measured by using selective autonomic blockade.

Experiment IV to evaluate the baroreflex sensitivity in adult rabbits rendered hypertensive.

Aging in male rabbits was associated with preserved base line level of BP, HR, RR and VNA.

While, "SNA was significantly increased in old versus adult and middle aged groups respectively.

Phenylephrine injection produced a significant increase in BP and VNA and a significant decrease in HR, RR and SNA in the three age groups studied.

Old, middle aged and adult male rabbits had nearly similar magnitude of arterial BP response to phenylephrine and similar HR, RR, VNA and SNA responses to phenylephrine.

Baroreflex sensitivity was significantly increased after elevating BP with phenylephrine injection in the three age groups and was significantly decreased after receptor blockade with either atropine or propranolol in the three age groups and the major portion of the decrease was due to the parasympathetic nervous system.

In rabbits rendered hypertensive, baroreflex sensitivity was significantly decreased after .elevating the BP by phenylephrine in comparison with normotensive control.

It can be concluded that indices of baroreflex function and baroreflex sensitivity were relatively well Assiut Vet.

Med.

J Vol 54 No.

118 July 2008 ntained in old rabbits.

Parasympathetic and sympathetic components of the ANS normally mediate the baroreflex in old age.

Baroreflex sensitivity is depressed in adult rabbits rendered hypertensive and with early signs of atherosclerosis.