Carlos J. Perec

Effects of an experimental diet on parotid saliva and dental plaque pH in institutionalized children

Sixty-six children aged 6-12, permanent residents of a childrens home, were placed on a diet during a 45-day experimental period to measure salivary flow-rate, pH of saliva and dental plaque, total concentrations of salivary proteins, inorganic phosphate, bicarbonate, calcium and amylase. The total caloric content, as well as the proportional nutrient and calorie distribution of the foods, were determined and compared with those of the previous habitual diet. After the experimental period, stimulated parotid salivary flow, increased by 40 per cent over the pre-experimental values. Total proteins of saliva and pH of both saliva and dental plaque increased significantly, whereas inorganic phosphate concentration decreased. Concentrations of bicarbonate, calcium and amylase did not differ from those found pre-experimentally. The findings appear to derive from lesser retention and increased hardness of the foods in the experimental diet.

Evidence for the presynaptic location of the alpha-adrenoceptors which regulate noradrenaline release in the rat submaxillary gland

SummaryFifteen days after duct ligation, the wet weight of the rat submaxillary gland was reduced to 40% of the contralateral control. Under these experimental conditions, the noradrenaline (NA) content expressed as μg/g was 1.2±0.1 in the control glands and 1.9±0.2 in the atrophied glands.The accumulation of 3H-NA in the tissue expressed as μCi/gland, did not differ when the atrophied glands were compared with the corresponding controls. Consequently, the uptake and retention of 3H-NA was not modified by the atrophy of the secretory cells of the gland.The spontaneous efflux of radioactivity from normal and atrophied submaxillary glands prelabelled with 3H-NA was similar. The analysis of the metabolic pattern in both experimental groups revealed that in the spontaneous outflow and also during potassium-induced depolarization, the formation of the O-methylated metabolite, 3H-normetanephrine (NMN) was reduced by more than 50% in the atrophied glands. During depolarization induced by K+, a 2-fold increase in the outflow of the deaminated glycol 3H-3,4-dihydroxyphenylglycol (DOPEG) was observed.The effect of phentolamine on the release of radioactivity induced by 60 mM K+ in normal and in atrophied submaxillary gland slices prelabelled with 3H-NA was also investigated. In both experimental groups, the fractional release of total radioactivity induced by K+ was similar. Phentolamine, 3.1 μM, produced a 3-fold increase in the fractional release of radioactivity both in the control and the atrophied glands. These results indicate that the increase of K+-induced release of 3H-NA induced by phentolamine was independent of the presence or absence of the postsynaptic structures. It is concluded that phentolamine increases transmitter release by blocking alpha-adrenoceptors located in the noradrenergic nerve endings of the rat submaxillary gland.

Effects of 6-hydroxydopamine treatment at birth on the submaxillary gland of the rat

SummarySix and 18 months after neonatal administration of 6-hydroxydopamine or surgical sympathetic denervation the submaxillary gland of the rat showed a marked depletion of noradrenaline stores. Six months after removal of the superior cervical ganglion the glands endogenous noradrenaline was lowered to 0.032±0.004 μg/g while after neonatal 6-hydroxydopamine the values were 0.228±0.023 μg/g (controls 2.145±0.382 μg/g). Eightheen months after either type of sympathetic denervation the neurotransmitter was still depleted. In rats treated with 6-hydroxydopamine the sialagogue effect of injected noradrenaline was potentiated 2.7-fold while the potentiation of the effect of noradrenaline was 3.6 times after surgical denervation. The magnitude of the supersensitivity developed to isoprenaline did not differ between both types of denervation. No supersensitivity to the cholinomimetic agent, methacholine, was observed. Cocaine administration or removal of the superior cervical ganglion slightly increased the supersensitivity to noradrenaline in rats treated with 6-hydroxydopamine. Eighteen months after surgical or chemical denervation, the activity of choline-acetyltransferase in the submaxillary gland was increased by about 50%. Of the respiratory enzymes studied, succinic dehydrogenase, fumarase and cytochrome oxidase, the activity of only the latter was markedly reduced by chronic sympathetic denervation. From the results obtained it is concluded that neonatal treatment with 6-hydroxydopamine causes a permanent and almost complete sympathectomy of the submaxillary gland of the rat.

Effects of sympathectomy on the in vitro α and β-responses of the parotid gland

SummarySalivary secretion in response to noradrenaline and isoprenaline was measured in innervated and chronically sympathectomized parotid glands of the rat. In innervated glands, the responses to isoprenaline lasted longer than those to noradrenaline. Chronic sympathetic denervation enhanced the responses to both noradrenaline and isoprenaline. The magnitude of the supersensitivity to isoprenaline was related to the dose and the time at which the responses were analyzed. Supersensitivity was greater for the initial than for the total secretion elicited by isoprenaline. Propranolol (1 mg/kg) and phenolamine (5 mg/kg) were used in order to determine the relative participation of α and β-adrenoceptors in the enhanced responses to isoprenaline. The results suggest that postjunctional supersensitivity for the secretory responses of this organ to isoprenaline is mainly mediated through β-adrenoceptors of the secretory cells and α-adrenoceptors of the myoepithelial cells.

Calcium in Salivary Glands of the Rat After Autonomic Denervation

Parasympathetic denervation reduced the size of the submandibular and major sublingual glands of the rat by about 30%. Calcium concentration was unchanged in the submandibular gland, but was reduced significantly in the sublingual gland. Sympathetic denervation elicited an increase in calcium concentration in the submandibular gland but not in the sublingual gland. Weight of the submandibular gland was reduced slightly, but that of the sublingual gland was not modified. After combined parasympathectomy and sympathectomy, both glands showed a significant decrease in size and calcium concentration.

Effects of guanabenz and guanfacine on postsynaptic α2-adrenoceptors in the rat submaxillary and parotid glands

SummaryThe effects of two α2-agonists (guanfacine and guanabenz) on both the submaxillary and parotid gland of the rat were studied. Whereas guanfacine in doses ranging between 1,000 and 30,000 μg/kg i.v. produced an immediate and persistent secretion of saliva from the submaxillary gland, guanabenz in doses as high as 40,000 μg/kg did not induce measurable secretion either from the parotid or the submaxillary gland. Secretion clicited by guanfacine was not modified by yohimbine (300 μg/kg) but was abolished by prazosin (100 μg/kg).In both glands, low doses of either guanabenz (10 μg/kg) or guanfacine (100 μg/kg) markedly inhibited the secretory responses induced by noradrenaline, methacholine and substance P, but not that induced by isoprenaline. The inhibition caused by the α2-agonists was greater for noradrenaline than for either methacholine or substance P. Blockade of α2-adrenoceptors with yohimbine (300 μg/kg) did not modify the response to noradrenaline, methacholine or substance P in either gland. However, the same dose of yohimbine injected 5 min before the α2-agonists prevented the inhibitory effects of guanfacine and guanabenz on the response induced by either one of the three sialagogic agents. Guanabenz (10 μg/kg) did not modify the increase in mean blood pressure observed after the different doses of noradrenaline employed to induce salivary secretion. Guanabenz (10 μg/kg) and guanfacine (100 μg/kg) did not change the time course of the secretion elicited by either noradrenaline, methacholine or substance P, since the degree of inhibition was of similar magnitude at all the periods of time analyzed.The results obtained give further support to the hypothesis that activation of α2-adrenoceptors in the submaxillary as well as parotid gland of the rat inhibits secretory responses which are mediated by either muscarine, substance P and α1-receptors and not those elicited by β-adrenoceptors.

Potassium-evoked efflux of [3H]purines from the rat submaxillary gland

1. Normal, atrophied and denervated submaxillary glands were incubated with [3H]adenine for 1 h. The accumulation of [3H]adenine, expressed as microCi/g tissue, did not differ significantly when the sympathetically denervated glands were compared with the control group. The radioactivity retained in both control and denervated tissues was also similar. 2. In atrophied glands 3H-accumulation as well as 3H-retention were 2-fold higher than these obtained in controls per unit weight, but 30% lower when expressed per gland. 3. The spontaneous efflux of radioactivity, expressed as fractional release, from normal, atrophied and denervated glands prelabelled with [3H]adenine was similar. 4. The outflow of radioactivity was enhanced by exposure of the tissues to 60 mM K+ during 2.5 min. 5. In all three groups, the purine release induced by K+ was the same. 6. Phentolamine 3.1 microM enhanced the K+-induced release of [3H]purine compounds in control and atrophied glands but not in denervated glands. 7. Propranolol 0.3 microM produced no changes among the three experimental groups. 8. Atropine 1 microM and phentolamine 3.1 microM plus atropine 1 microM did not modify the release of tritiated purine compounds in control and denervated glands. 9. Our results cannot discriminate between neuronal or non-neuronal elements as the source of purines released by depolarization but suggest that classical pharmacological tools such as phentolamine and atropine may affect purine metabolism in a complex fashion.

Delay by bretylium of adrenergic nerve degeneration after sympathectomy of the submaxillary gland

Administration of 24 mumol/kg of bretylium 10 h after ganglionectomy delayed the loss of endogenous norepinephrine and the impairment of neuronal uptake of 3H-metaraminol (3H-MA) that follow sympathetic denervation. This delay was evident 16 and 20 h after denervation. Twenty four h after ganglionectomy, when NE stores and uptake of 3H-MA were reduced to their lowest values in untreated rats, in bretylium-treated ones these values were approximately 40% of those in normal glands. The onset of degeneration secretion in treated rats was delayed by about 9 h. The development of prejunctional supersensitivity was also delayed. The subcellular distribution of NE in normal and 16 h denervated glands showed that denervation reduced the neurotransmitter to the same extent in the 3 fractions: coarse, supernatant and microsomal. Treatment with bretylium and pargyline prevented the loss of NE from the microsomal fraction. Previous administration of pargyline antagonized the protection of 3H-MA uptake seen in 28 h denervated rats treated with bretylium. However, this drug combination induced a greater retention of endogenous NE 24 h after denervation. Bretylium inhibited intraneuronal MAO by 40%. It is concluded that bretylium treatment can delay the degeneration of adrenergic nerve terminals separated from the cell bodies by a pharmacological effect probably not related to MAO inhibition or to its neurone blocking action.

Secretory effects of 6-hydroxydopamine in normal and denervated submaxillary glands of the rat

SummaryInjection of 6-hydroxydopamine (6-OH-DA) elicited a marked and sustained secretory response of control and surgically sympathectomized submaxillary glands of rats. These responses were diminished by previous treatment with reserpine 0.1 mg/kg 48 and 24h before the experiment and almost abolished by 5 mg/kg reserpine 6 h before the administration of 6-OH-DA. The responses to 6-OH-DA were potentiated in control glands by previous preganglionic denervation of either the parasympathetic or sympathetic nerves of the gland. Development of postjunctional supersensitivity in denervated glands also increased the responses to 6-OH-DA, while atropine had a feeble blocking action. For all these responses, the adrenal catecholamines played no role. After two consecutive doses of 6-OH-DA a third dose of the drug still elicited a secretory response that was 50% of that of the first dose.It is concluded that for the responses to 6-OH-DA the leakage of noradrenaline from the degenerating adrenergic nerve endings of the submaxillary gland plays a partial role. Noradrenaline released by the drug from other tissues and reaching the gland via the circulation also contributes to the responses observed. A muscarinic component may also participate in the secretory effects of 6-OH-DA.

Electron microscopic evidence that bretylium and pargyline delay adrenergic nerve degeneration after sympathectomy of the pineal gland

SummarySeventeen and twenty four hours after sympathetic denervation, noradrenaline stores of the rat pineal gland were depleted to 50% and 10% of controls, respectively. Electron microscopic studies showed the coexistence of normal and altered nerve endings 17 h after denervation, while 24 h after denervation, only degenerated nerve terminals were observed.Treatment with pargyline (512 μmoles/kg) or bretylium (24 μmoles/kg) significantly delayed the loss of noradrenaline from denervated glands. In pargyline treated rats, 17 h after denervation, noradrenaline stores were 90% of control glands. After bretylium, values obtained 24 h after denervation, declined to 36% of innervated glands. Persistence of neurotransmitter coincided with the presence of normal nerve endings as observed electron microscopically.It is concluded that both, pargyline and bretylium, prolonged the survival of nerve endings severed from the cell body.