Effect of corticosterone and triiodothyronine on (Na+ + K+)-adenosine triphosphatase activity in rat submandibular gland

Expression of Na(+)/K(+)-ATPase alpha subunit isoforms in rat salivary glands: occurrence of sense and antisense RNAs of the alpha3 isoform in the sublingual gland

We examined the expression of Na(+)/K(+)-ATPase alpha-subunit isoforms in rat salivary glands by RT-PCR. Isoform alpha1 was expressed strongly in all three major salivary glands. The alpha2 isoform was expressed in both submandibular gland (SMG) and sublingual gland (SLG) but faintly in the parotid gland (PG). The alpha3 was detected only in the SLG, and the alpha3 mRNA in the SLG was 1/8 of its level in the brain. Na(+)/K(+)-ATPase alpha3 isoform in the SLG, was localized predominantly on the basolateral plasma membranes in serous cells by immunohistochemical method. We also found the presence of natural antisense RNA of the alpha3 isoform in rat SLG: the 1st-strand cDNA prepared with gene-specific forward primers targeted to the CDS region and to the promoter region of the alpha3 gene in place of oligo(dT) or gene-specific reverse primers produced reasonable PCR products corresponding to the alpha3 cDNA sequence by the subsequent PCR reaction. Synthesis of the 1st-strand cDNA with the gene-specific forward primers was prevented by RNase digestion of the total RNA preparation, indicating that the PCR products in the RT-PCR system were not due to the contaminated genomic DNA, if any. The alpha3 protein level in rat SLG increased with aging, and levels of both alpha3 mRNA (sense RNA) and alpha3 antisense RNA were higher in SLGs of aged rats than in those of young rats, respectively.

Regulation of rat renal (Na(+) + K+)-adenosine triphosphatase mRNA levels by corticosterone

We investigated the mechanisms for glucocorticoid regulation of rat renal NaK-ATPase activity. Our findings suggest that the magnitudes of corticosterone-induced increases in alpha 1 mRNA and beta 1 mRNA levels are similar in the kidney of the adult adrenalectomized rats. The results also suggest that corticosterone restores NaK-ATPase activity in adrenalectomized rats prior to any enhanced sodium delivery.

Effects of thyroxine and dexamethasone on rat submandibular glands

Glucocorticoids and thyroxine are known to have a marked effect on the flow rate and protein composition of rat parotid saliva in hormonally intact animals. In the present study, the effects of a one-week treatment of male rats with dexamethasone and thyroxine were studied by electron microscopy and x-ray micro-analysis, and by measurement of the flow rate and determination of the chemical composition of pilocarpine-induced submandibular saliva. Thyroxine had the most extensive effects on the submandibular gland. The acinar cells were enlarged and filled with mucus; the cellular calcium concentration was significantly increased. The flow rate of the submandibular saliva was significantly reduced compared with that in saline-injected control animals. Thyroxine caused an increase in the concentrations of protein, total calcium, and potassium in the saliva. Dexamethasone had no significant effects on gland ultrastructure or on the elemental composition of the acinar cells; flow rate was not affected, but the concentrations of protein, calcium, and potassium were significantly increased. The effects of dexamethasone and thyroxine on the flow rate and protein composition of pilocarpine-induced rat submandibular saliva differ from those reported earlier for rat parotid saliva after simultaneous stimulation with pilocarpine and isoproterenol.

Dexamethasone and adrenalectomy alter brain (Na+,K+)-ATPase responses to noradrenergic stimulation or depletion

We investigated the effects of adrenalectomy or dexamethasone treatment on the regulation of brain (Na+,K+)-ATPase by noradrenaline. Noradrenergic stimulation was produced by repeated injections of yohimbine, and noradrenaline depletion by an injection of the selective toxin DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine). Adrenalectomy had no effect on the number of ouabain binding sites in cerebral cortex, but increased the number of sites synergistically with noradrenergic stimulation. Dexamethasone prevented the decrease in ouabain binding in rats treated with DSP4, but did not itself alter ouabain binding. Neither dexamethasone nor adrenalectomy altered the changes in beta-receptor binding associated with the noradrenergic manipulations. Changes in exposure to corticosteroids may alter the coupling between adrenoceptor binding and second messenger activation in a way that affects (Na+,K+)-ATPase regulation.

Effect of triiodothyronine on system A amino acid transport in cells of rat submandibular gland

The effect of L-3,5,3'-triiodothyronine (T3) on alpha-aminoisobutyric acid (AIB) transport in isolated cell suspensions of rat submandibular gland was investigated. The uptake of ATB by these cells appeared to require extracellular Na+ and was inhibited by ouabain (10(-3) M). Cell suspensions from thyroidectomized rats which have been given three successive doses of T3 on alternate days (50 micrograms/100 g BW) showed a significant increase in AIB uptake compared with cells isolated from thyroidectomized rats treated with diluent. Efflux of AIB from the cell suspension was not affected by T3. There was no significant changes in AIB uptake 12 h after a single injection of T3 (50 micrograms/100 g BW). However, there was a significant 49% and 65% increase in AIB net uptake at 24 and 48 h, respectively, after T3 treatment. Under similar conditions, the cell suspension showed a 48% increase in NaK-ATPase activity at 12 h and to a peak of 61% at 24 h. Therefore, changes in NaK-ATPase activity preceded the changes in AIB net uptake upon treatment with T3, implying that AIB uptake is probably mediated, at least in part, by the activity of NaK-ATPase.

Action of compounds with effective in vivo mineralocorticoid activity on ion transport in leucocytes

We have studied the in vitro short-term effects of aldosterone (1.0-1000 nmol l-1), cortisol (0.5-5.0 mumol l-1), fludrocortisone (1.0-10 nmol l-1) and carbenoxolone (0.5-3 mmol l-1) on 86rubidium influx (a model for potassium), 22sodium efflux, and [3H]-ouabain binding capacity in intact human leucocytes. No effect of aldosterone (at concentrations present in Conn's syndrome) or fludrocortisone could be demonstrated on cation fluxes or [3H]-ouabain binding compared to controls. No significant effect of cortisol, at concentrations either physiological or present in Cushing's syndrome, could be demonstrated on cation fluxes or [3H]-ouabain binding compared to controls. Carbenoxolone significantly increased 86Rb influx and 22Na efflux at concentrations known to cause hypokalaemia in man. The effect was not blocked by propranolol. No effect could be demonstrated for [3H]-ouabain binding.