Circadian rhythm and neural regulation of rat pineal angiotensin converting enzyme

Angiotensin converting enzyme was detectable in rat pineal gland and exhibited a circadian rhythm in activity with maximum at the end of the light phase of daily photoperiod. Superior cervical ganglionectomy (SCGx) or exposure to light for 6 days increased enzyme activity and obliterated morning-evening differences, whereas injection of the beta-agonist isoproterenol depressed the high values observed in SCGx animals. These results indicate that angiotensin converting enzyme in the pineal gland is under negative control by the norepinephrine released from pineal sympathetic nerves.

Changes in drinking behavior caused by superior cervical ganglionectomy and pinealectomy in rats

The effect of superior cervical ganglionectomy (SCGx) or pinealectomy (Px) on drinking behavior was examined in rats subjected to a restricted photoperiod (i.e. 4 h of light per day). Both in male and female rats SCGx depressed water intake significantly from 1 to 3 days after surgery. After osmolar (i.p. 5% NaCl) or non-osmolar stimuli (s.c. isoproterenol) SCGx female rats exhibited a depressed response in water and NaCl intake, an effect not observed in male rats. Castration of male or female rats did not change their drinking behavior response to thirst stimuli. Px did not mimic SCGx in its effects on drinking behavior; moreover in sham-Px rats the water intake fell significantly after craniotomy. Following the injection of isoproterenol or i.p. hypertonic saline, the drinking behavior was the same in Px or sham-Px animals. To assess whether the effects of SCGx needed the presence of the pineal gland, Px or sham-Px rats were subjected to SCGx 9 days later. In both groups SCGx depressed water intake; however the inhibition that followed ganglia removal in Px rats was greater than that observed in animals with a pineal gland. Water and NaCl intake following isoproterenol or i.p. hypertonic saline were similar in both experimental groups. These results suggest that SCGx affects drinking behavior in part by pathways other than pineal denervation.

Angiotensin regulates release and synthesis of serotonin in brain

Angiotensin II released serotonin from neuron terminals and accelerated synthesis of the serotonin. This increase in synthesis depended on the activation of tryptophan hydroxylase. A biphasic effect was observed: at high doses the stimulatory effect depended on conversion of angiotensin II to angiotensin III. At low doses an inhibitory effect was found, possible dependent on an angiotensin II metabolite. These actions represent a subtle regulation of the open-loop serotonin system.

A pressor substance in the cerebrospinal fluid of normotensive and hypertensive patients

A pressor polypeptide was isolated from the cerebrospinal fluid of normotensive and hypertensive patients. Pharmacologically it behaves like angiotensin I. A very significant correlation (r = 0.83, P < 0.001) was found between the concentration of this polypeptide and the blood pressure of essential hypertensive patients.

Angiotensin and renin in rat and dog brain

An enzyme with the characteristics of classical renin was isolated from brain extracts of nephrectomized dogs. This enzyme is thermolabile, nondialyzable, and forms a vasoconstrictive material when incubated with renin plasma substrate at pH 7. A short lasting pressor activity was also found in brain extracts of dogs and rats. This activity was due to a substance identified by chemical and pharmacological tests as angiotensin. Countercurrent distribution of brain extracts of rats showed that 38% of the pressor activity corresponded to angiotensin II and the remainder to angiotensin I. A remarkable correlation was found between angiotensin and norepinphrine concentrations in different portions of the encephalon of the dog.