[Augmentation of clonidine on Bezold-Jarisch reflex control of renal sympathetic nerve activity in cats].

The present study was undertaken to examine the possible augmentation of clonidine on the control of renal sympathetic nerve activity by Bezold-Jarisch reflex in anesthetized cats. Veratrine (3-20 micrograms/kg) produced dose-dependent decreases in arterial blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RNA). Clonidine (3 micrograms/kg) resulted in decreases in BP, HR and RNA. Clonidine significantly potentiated the influence of Bezold-Jarisch reflex on RNA, but did not potentiate the influence of Bezold-Jarisch reflex on BP and HR. Bezold-Jarisch reflex gain calculated as percent inhibition of renal sympathetic nerve activity divided by decreases in mean blood pressure was significantly higher after the administration of clonidine.

[The renal nerve and cardiovascular responses to renal receptor stimulation with veratrine in dogs].

Renal nerve and cardiovascular effects of intrarenal veratrine (Ver) were investigated using the cross-perfused kidney preparations of anesthetized dogs. Ver (1 and 3 micrograms/kg), injected as a bolus, elicited increases in arterial blood pressure (ABP), heart rate (HR) and renal efferent nerve activity (RENA). Ganglion blockade, hexametonium (2 mg/kg) markedly diminished increases in ABP, HR and RENA induced by Ver. In a separate group of animals, significant increases in renal afferent nerve activity (RANA) occurred after Ver administration. It is concluded that selective intrarenal Ver activates renal nerve afferents, and these results in cardiovascular changes are consistent with efferent sympathetic activation.

Clinical effects of local application of collagen film-immobilized tetracycline.

Tetracycline-containing cross-linked collagen film (TC film), or tetracycline-free placebo film, were locally applied 4 times, at 1-week intervals, to 33 teeth with periodontal pockets larger than 4 mm, in 11 patients with periodontal disease. The clinical and microbiological effects are summarized, as follows. In the group treated with the TC film, (1) the clinical indices were significantly decreased at the 4th and 7th weeks in comparison with those at the beginning of treatment. In particular, this group showed a significant decrease in the incidence of bleeding as compared with the placebo group at the 4th week. (2) Total counts of bacteria in the periodontal pockets showed an obvious tendency to decrease with time. The proportion of black-pigmented bacteroides was significantly decreased at the 4th and 7th weeks when compared with the pretreatment value. The extent of decrease in the proportion of spirochetes at both the 4th and 7th weeks was significant compared with the placebo group and the pretreatment value.

Application of a local drug delivery system to periodontal therapy: I. Development of collagen preparations with immobilized tetracycline.

For the purpose of applying a local drug delivery system to periodontal therapy, atelocollagen preparations with immobilized tetracycline (TC) were prepared by modifying the form of the collagen, the concentration of the immobilized TC, and the time of the cross-link process with glutaraldehyde. The course of the TC release from the collagen preparations into an aqueous solution was determined in relation to time. The preparations were also inserted into periodontal pockets, and the amount of TC remaining in the pocket was determined daily. The results obtained were as follows: 1) The degree of drug release could be controlled to some extent by adjusting the TC concentration and the time of the cross-link process; and 2) an amount of TC exceeding the effective dose in the gingival crevicular fluid was present in the periodontal pocket even 10 days after the insertion of TC fixed in the cross-linked processed collagen film in the periodontal pockets.

Renal nerve and cardiovascular responses to cardiac receptor stimulation in rabbits.

It has been shown that a species difference exists among cats, dogs, and monkeys in the reflex response to cardiac sympathetic afferent stimulation with bradykinin (BK). This study was performed to determine the arterial blood pressure (ABP), heart rate (HR), and renal nerve activity (RNA) responses to epicardial BK applications in the intact and sinoaortic-denervated and vagotomized (SAD + Vx) rabbits. Eight rabbits were anesthetized with pentobarbital sodium. The heart was exposed and suspended in the epicardial cradle. The ABP, HR, and RNA responses were determined when 1 and 10 micrograms/ml BK were applied to the anterior surface of the left ventricle in the intact and SAD + Vx state. In both the intact and SAD + Vx rabbits, ABP, HR, and RNA were significantly reduced with epicardial BK. In the SAD + Vx rabbits, BK evoked small decreases in ABP and HR and no change in RNA after topical lidocaine. These results show the existence of a depressor response and decreases in HR and RNA in the rabbit mediated by the action of BK on cardiac sympathetic afferents.

Renal mechanoreceptors in nonhuman primates.

The present experiments provide the first description of the afferent discharge characteristics of renal mechanosensitive receptors in the nonhuman primate. Twenty-seven single units with mechano-sensitive receptor activity were obtained. Afferent discharge occurred regularly (pulse synchronous) or irregularly (pulse asynchronous) under spontaneous respiration. The activity of pulse synchronous units was increased by partial occlusion of the renal vein and elevation of arterial pressure. Impulse activity decreased or disappeared during bleeding or renal arterial occlusion. The impulse activity of pulse asynchronous units was increased by partial occlusion of the renal vein. The impulse activity of silent units was induced only by partial occlusion of the renal vein. An increase in ureteral pressure (50 mmHg) produced an increase or induced impulse activity in only three of the 27 fibers tested. Compression of the kidney or renal venous occlusion was associated with a decrease in systemic arterial pressure, whereas renal arterial occlusion produced a rise in systemic arterial pressure. An increase in ureteral pressure (50 mmHg) did not produce a change in arterial pressure.

Blood volume changes and high and low pressoreceptor activity in cats.

Studies were undertaken in the cat to determine if moderate hemorrhage or volume expansion significantly altered carotid sinus and aortic baroreceptor activity. In addition, the experimental design provided the opportunity to compare gain of the two sets of receptors. A 20% blood volume expansion increased mean arterial blood pressure 5.2% and carotid sinus nerve activity 14.7%, whereas a 20% hemorrhage decreased mean arterial blood pressure 10.8% and carotid sinus nerve activity 32.3%. For the aortic baroreceptors, a 20% blood volume expansion increased mean arterial blood pressure 5.9% and nerve activity 10.5%, and a 20% hemorrhage decreased mean arterial blood pressure 8.9% and nerve activity 21.0%. The blood pressure-discharge curves for the carotid sinus and aortic baroreceptors were not different. The well-known high sensitivity of atrial receptors was also documented. We conclude that both high- and low-pressure receptors apprise the central nervous system of the status of intravascular volume and pressure.

Comparison of carotid sinus baroreceptors in dogs, cats, monkeys, and rabbits.

Single-unit recordings were obtained from the vascularly isolated Krebs-Henseleit-perfused carotid sinus of the rabbit and cat, and the results were compared with those obtained previously from the monkey and dog. Carotid sinus pressure was altered using static pressure steps. There was a highly significant correlation between resting arterial pressure and carotid sinus baroreceptor threshold pressure. The baroreceptors of the monkey and rabbit had a significantly lower threshold than those of the dog and cat. The baroreceptors of the monkey had a significantly lower gain than those of the three nonprimates. This is the first study in which baroreceptor activity has been studied under the same experimental conditions in four different species.

Changes in cardiac myofibrillar ATPase activity during development of hyperthyroidism in the rabbit.

This study examined changes in cardiac myofibrillar ATPase activity during the development of hyperthyroidism and the relationships between changes in myofibrillar ATPase activity and hemodynamic parameters in rabbits. Calcium-stimulated, magnesium-dependent ATPase (Ca-ATPase) activity of cardiac myofibrils exhibited about a 30% increase after the first week of treatment with excess desiccated thyroid tissue powder (thyroid-treatment) and did not show further increase during thyroid-treatment. Development of cardiac hypertrophy and increases in systolic and diastolic blood pressure were dependent upon prolonged periods of thyroid-treatment lasting from 3 days to 4 weeks, whereas the maximal increase (about 55%) in heart rate was seen after the first week of thyroid-treatment. The elevated level lasted throughout subsequent thyroid-treatment. Lineweaver-Burk plots showed an increase in Km and Vmax values for Ca-ATPase activity of myofibrillar preparation from the thyrotoxic hearts of treated animals. Increased Ca-ATPase activity was correlated with thyroid-induced changes in heart rate. Propranolol partially reduced the thyroid-induced increase in Ca-ATPase activity and heart rate, suggesting participation of beta-adrenoceptors in the thyroid-induced increases of Ca-ATPase activity and heart rate.

Carotid sinus baroreceptor activity in the nonhuman primate.

The carotid sinus of eight adult Macaca fascicularis monkeys was functionally isolated from the circulation and perfused with Krebs-Henseleit solution. The impulse activity in 65 carotid sinus baroreceptor fibers from the left carotid sinus nerve was studied during nonpulsatile perfusion and was compared with the impulse activity in 68 fibers from 10 adult mongrel dogs. Curves relating the discharge frequency to carotid sinus pressure were constructed. The baroreceptor fibers of the monkey had a significantly lower threshold, gain, pressure at the point of inflection, and plateau pressure than those of the dog. Hysteresis, as indicated by the separation of the stimulus-response curves obtained by increasing and then decreasing carotid sinus pressure, was observed. At any given pressure, the discharge frequency of baroreceptors was greater when carotid sinus pressure was increased than when it was decreased in both species. These results provide direct evidence that carotid sinus baroreceptors in the monkey are less sensitive to pressure changes than those in the dog.

Comparison of carotid sinus baroreceptor sensitivity in newborn and adult rabbits.

The impulse activity in single baroreceptor fibers of the carotid sinus nerve to the carotid sinus was studied in newborn rabbits (9--11 days old) during nonpulsatile perfusion of in vitro carotid sinus preparations. Results were compared with those obtained from adult rabbits. Seventy-eight baroreceptor fibers from 10 newborn rabbits showed lower threshold pressure (54.6 +/- 2.5 mmHg) than that of 59 fibers from adult rabbits (74.2 +/- 4.1). The gain of 14 baroreceptors from newborn rabbits (0.62 +/- 0.07 impulses . s-1 . mmHg-1) was higher than that of 21 baroreceptors from adult rabbits (0.38 +/- 0.03). Results provided direct evidence that carotid sinus baroreceptors in the newborn animals were more sensitive to pressure changes than those in the adult. It is suggested that depressed baroreceptor reflex activity previously observed in most newborn animals is not due to underdeveloped afferent activity of the baroreceptors but to other mechanisms including the efferent control systems.