SULFONAMYL DIURETICS--MECHANISM OF ACTION AND THERAPEUTIC USE.
The mechanism whereby sulfonamyl diuretics are effective is through the blockage of the renal tubular reabsorption of chloride. The excretion of sodium, potassium and water is a passive one to maintain ionic equilibrium. Chlorothiazide has been shown to be almost ineffective as a diuretic agent per se. Although it does block a moiety of the renal tubular reabsorption of bicarbonate, the effect is merely a transient one. (+info)
The interactions of thiazide diuretics with parathyroid hormone and vitamin D. Studies in patients with hypoparathyroidism.
In order to clarify the mechanisms of thiazide diuretic-induced hypocalciuria, the effect of a thiazide was studied for 7 days in seven patients with hypoparathyroidism on Vitamin D and one on calcium infusion, and seven euparathyroid patients with hypercalciuria. In the control group, calcium excretion (mg/24 hr) fell by 44% from 415 to 232 within 4 days and remained at this level. Plasma total calcium corrected for total protein did not change. In the hypoparathyroid group, calcium excretion fell by 11% from 351 to 311 and then returned to the base line level. Plasma total calcium (mg/100 ml) increased from 10.09 to 10.88, 11.29 and 10.77 at the end of the 2nd, 4th, and 7th day of thiazide administration. In the patient having i.v. calcium and no Vitamin D, neither plasma nor urinary calcium changed significantly. In both groups sodium excretion increased on the first 2 days and fell to or below base line level thereafter. Urinary phosphate, magnesium, and potassium increased, plasma phosphate rose, and magnesium and potassium fell. It is concluded that: (a) The hypocalciuric effect of thiazides requires the presence of parathyroid hormone and is not solely a result of sodium depletion. (b) The hypercalcemic effect of thiazides in hypoparathyroidism is due to increased release of calcium from bone and requires the presence of a pharmacologic dose of Vitamin D. (c) Thiazides enhane the action of parathyroid hormone on bone and kidney; Vitamin D can replace parathyroid hormone in this interaction in bone but not in kidney. (+info)
A comparative study of the action of frusemide and methyclothiazide on renin release by rat kidney slices and the interaction with indomethacin.
1 The effects of frusemide (a diuretic acting on the loop of Henle) and methyclothiazide (a thiazide diuretic) on renin release were studied on rat kidney slices. 2 Frusemide at concentrations of 1.5 and 7.5 mmol/l produced significant increases in renin release but had no effect at 0.15 mmol/l. 3 Methyclothiazide in a similar concentration range did not increase renin release; instead, at the highest concentration used, methyclothiazide (3.5 mmol/l) inhibited renin release. 4 Indomethacin (25 mumol/l) did not inhibit the increase of renin induced by frusemide. 5 Our limited study in vitro is consistent with the findings of other workers who have shown in vivo, in the absence of systemic electrolyte depletion, that only "loop diuretics" increase renin secretion. Under our experimental conditions, it is suggested that frusemide exerts a direct action either upon the epithelioid cells or upon the macula densa since the renal prostaglandin system does not intervene. (+info)