Mechanism of chlorpropamide action in diabetes insipidus

Central Diabetes Insipidus Masked by Uncontrolled Diabetes Mellitus: A Challenging Case Managed With Indapamide

A 44-year-old man with a history of traumatic brain injury (TBI) presented to the emergency room (ER) with diabetic ketoacidosis (DKA). After resolution of DKA, the patient had persistent polyuria (up to 5.5 L/24 h) associated with low specific gravity (1.002-1.005) and severe hypernatremia (up to 186 mmol/L) that led us to consider the possibility of central diabetes insipidus (DI). Due to the lack of desmopressin availability in our country, we managed the patient using indapamide. Polydipsia and polyuria in a patient with controlled diabetes mellitus (DM) should raise suspicion for alternative etiologies, including DI. Appropriate fluid management during hospitalization is critical to avoid life-threatening complications. TBI is an important cause of central DI and should be treated with desmopressin, an arginine-vasopressin (AVP) analog. In the absence of desmopressin, alternative options can help patients with central DI, including thiazides, carbamazepine, chlorpropamide, among others less studied.

Lead Optimization Resources in Drug Discovery for Diabetes

BACKGROUND

Diabetes, defined as a chronic metabolic syndrome, exhibits global prevalence and phenomenal rise worldwide. The rising incidence accounts for a global health crisis, demonstrating a profound effect on low and middle-income countries, particularly people with limited healthcare facilities.

METHODS

Highlighting the prevalence of diabetes and its socio-economic implications on the population across the globe, the article aimed to address the emerging significance of computational biology in drug designing and development, pertaining to identification and validation of lead molecules for diabetes treatment.

RESULTS

The drug discovery programs have shifted the focus on in silico prediction strategies minimizing prolonged clinical trials and expenses. Despite technological advances and effective drug therapies, the fight against life-threatening, disabling disease has witnessed multiple challenges. The lead optimization resources in computational biology have transformed the research on the identification and optimization of anti-diabetic lead molecules in drug discovery studies. The QSAR approaches and ADMET/Toxicity parameters provide significant evaluation of prospective "drug-like" molecules from natural sources.

CONCLUSION

The science of computational biology has facilitated the drug discovery and development studies and the available data may be utilized in a rational construction of a drug 'blueprint' for a particular individual based on the genetic organization. The identification of natural products possessing bioactive properties as well as their scientific validation is an emerging prospective approach in antidiabetic drug discovery.

Chlorpropamide upregulates antidiuretic hormone receptors and unmasks constitutive receptor signaling

The mechanism by which chlorpropamide (CP) treatment promotes antidiuresis is unknown. CP competitively inhibited antidiuretic hormone (ADH) binding and adenylyl cyclase (AC) stimulation (inhibition constants K(i) and K'(i) of 2.8 mM and 250 microM, respectively) in the LLC-PK(1) cell line. CP (333 microM) increased the apparent K(a) of ADH for AC activation (0.31 vs. 0.08 nM) without affecting a maximal response, suggesting competitive antagonism. Because CP lowers "basal" AC activity and the AC activation-ADH receptor occupancy relationship (A-O plots), it is an ADH inverse agonist. Twenty-four-hour CP exposure (100 microM) upregulated the ADH receptors without affecting affinity. This lowered K(a) and increased basal AC activity and maximal response (1. 86 vs. 1.35 and 14.9 vs. 10.6 fmol cAMP. min(-1). 10(3) cells(-1), n = 6, P<0.05). NaCl, which potentiates ADH stimulation, also increased basal AC activity. This, together with the CP-ADH inverse agonism and increased basal AC activity at higher receptor density, unmasks constitutive receptor signaling. The CP-ADH inverse agonism explains receptor upregulation and predicts the need for residual ADH with functional isoreceptors for CP-mediated antidiuresis. This could be why CP ameliorates partial central diabetes insipidus but not nephrogenic diabetes insipidus.

The molecular biology of human hereditary central diabetes insipidus

Molecular biology techniques have begun to shed light on the genetic basis of autosomal dominant central DI, but several very basic questions remain to be answered. The disorder was initially presumed to have a developmental, degenerative, or autoimmune basis based on the autopsy findings in the hypothalamus of a limited number of patients. The molecular cloning of the AVP-NP II gene and the clue from the Brattleboro rat that at least this one form of hereditary DI involved an AVP-NP II gene mutation allowed us to focus on this gene in our study of human hereditary DI. Our initial experiments did not show this gene to have a major structural alteration such as a deletion, insertion, or rearrangement, but the approach was not capable of detecting more suitable defects. The linkage studies provided substantial evidence that one particular OT-NP I haplotype was linked to the disease phenotype in each family, and thus, a mutation in the AVP/OT region of chromosome 20 is responsible for this disease. Ito et al. (1991) then identified a single base change in the AVP-NP II gene in affected members of one Japanese family. This change was not detected in unrelated, unaffected persons and thus is a good candidate for the mutation causing the disease in this family. However, there appears to be diversity in the molecular basis of autosomal dominant central DI as affected members of one of our families did not have this particular base change in either AVP-NP II allele and recently another distinct AVP-NP II gene base change has been associated with this disorder. One interesting question still to be addressed is how a mutation in the NP-II coding region of this gene prevents AVP release from the posterior pituitary in the rat or the human disease. Does the disrupted AVP-NP II coding sequence prevent normal processing of the mRNA so that it can not be properly translated into protein? Does the mutated AVP-NP II glycoprotein precursor protein interfere with normal post-translational processing to prevent release of AVP? Is an altered NP II protein not able to protect the AVP from proteolysis within the magnocellular neuron? An even more puzzling question is how a mutation in the gene encoding a hormone is inherited in an autosomal dominant pattern. The Brattleboro rat model follows the a priori expectation of autosomal recessive inheritance: the animal only exhibits a defect in hormone function if both genes encoding the hormone are defective.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of chlorpropamide on water and urea transport in the inner medullary collecting duct

The present in vitro microperfusion study examined whether chlorpropamide (CPM) has a direct effect on hydraulic conductivity (Lp x 10(-6) cm/atm.sec) and 14C-urea permeability (Pu x 10(-5) cm/sec) in the middle and distal inner medullary collecting duct (IMCD) obtained from acutely water-loaded Wistar rats and rats homozygous for diabetes insipidus (DI). CPM (10(-4) M) added to the bath fluid increased the Lp in the water-loaded Wistar rats from -0.05 +/- 0.13 to 6.25 +/- 0.74 (p less than 0.01) and in the DI rats from 0.05 +/- 0.01 to 5.95 +/- 0.84 (p less than 0.01), but had no effect when it was added to the perfusate. CPM stimulated Lp in a dose-dependent manner with the threshold effect at 10(-6) M. However, the addition of CPM (10(-4) M) to submaximal concentration of VP in the bath fluid did not increase the Lp. Furthermore, CPM was unable to block the inhibitory action of PGE2 on the vasopressin (VP)-stimulated Lp. On the contrary, PGE2 blocked the CPM-stimulated Lp. CPM (10(-4) M) in the peritubular fluid was able to cause a significant rise of the Pu from 13.5 +/- 0.8 to 17.3 +/- 1.0 reversibly, which represented 16% of maximum stimulated effect produced by 50 microU/ml of VP. Thus, pharmacological doses of CPM added to the peritubular side have a direct effect on terminal IMCD increasing water and urea permeability in the absence of VP, but this drug does not potentiate the VP-stimulated water transport in the IMCD. Our results were unable to confirm the hypothesis that CPM potentiates the VP-antidiuresis by the inhibition of PGE2 action in the rat IMCD.

Association of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. The Wolfram or DIDMOAD syndrome

Seven patients with a rare syndrome of diabetes insipidus (DI), diabetes mellitus (DM), optic atrophy (OA), neurosensory deafness (D), atony of the urinary tract, and other abnormalities (Wolfram or DIDMOAD syndrome) are reported. Of the seven patients, three siblings were followed up for 10-17 years. All seven patients had diabetes mellitus and optic atrophy; six had diabetes insipidus; and in the four patients investigated there was dilatation of the urinary tract. The severity of diabetes varied, and all required insulin for control of the hyperglycaemia. In one patient the course of the disease simulated maturity onset diabetes of the young; another presented with ketoacidosis; but none had haplotypes usually associated with insulin dependent diabetes mellitus. The diabetes insipidus responded to chlorpropamide, suggesting partial antidiuretic hormone deficiency. Onset of optic atrophy and loss of vision occurred relatively late and progressed slowly, although in one patient there was a rapid deterioration in visual acuity. Deafness was mild, of late onset, and of sensorineural origin. A degenerative process affecting the central and peripheral nervous system can explain all the manifestations of the syndrome except diabetes mellitus. The pathogenesis of the diabetes mellitus remains obscure.

Syndrome of inappropriate antidiuretic hormone secretion during cis-dichlorodiammineplatinum therapy in a patient with an ovarian carcinoma

Case report of syndrome of inappropriate antidiuretic hormone. (SIADH) developing in a patient treated with cis-dichlorodiamine platinum for an endometrioid carcinoma of the ovary. This syndrome has not been reported with this tumor type and no other drugs known to cause SIADH were administered.

Drug management of antidiuretic hormone imbalance following pituitary surgery

ADH imbalance may occur in patients after pituitary surgery. Two cases are presented that demonstrate the problems associated with the disturbance of water metabolism. The medical management of these patients is discussed, with emphasis on the importance of the correct choice of pharmacological agents to control the manifestations of ADH imbalance.

Idiopathic neurogenic diabetes insipidus in a cat

A 5-year-old, domestic long-haired cat was presented for examination because of polydipsia, polyuria and inappropriate urination of 3 months' duration. Neurogenic diabetes insipidus was diagnosed, based on hyposthenuria with failure to concentrate urine in response to water deprivation and positive response to antidiuretic hormone administration. Treatment with hydrochlorothiazide or chlorpropamide orally gave inadequate antidiuresis, but response to injections of vasopressin tannate in oil was sufficient for satisfactory management.

Syndrome of inappropriate antidiuretic hormone secretion following dis-dichlorodiammineplatinum II in a patient with malignant thymoma

A patient with malignant thymoma is reported, in whom the syndrome of inappropriate antidiuretic hormone secretion (SIADH) occurred 36-48 hours after being given cis-Dichlorodiammineplatinum II (CPPD) with a mannitol diuresis. The SIADH was treated by fluid restriction and demeclocycline and subsided after approximately 72 hours. Subsequent courses of CPPD with mannitol diuresis were given with demeclocycline prophylactically and no untoward effects noted. The precise mechanism for the SIADH following the use of CPPD is unknown, but may be life-threatening, especially since preloading with fluid followed by forced diuresis is used when CPPD is given to avoid nephrotoxicity. The patient has survived 37 months, with 24 months of relapse-free survival following treatment with CPPD, irradiation and surgery.

Factors moderating the effect of oral sulfonylureas on free water clearance

The effects of the antidiuretic agent chlorpropamide and the diuretic agent tolazamide on solute-free water clearance (CH2O) were compared in noninsulin-dependent diabetic patients undergoing water diuresis. Hyperglycemia (fasting serum glucose above 200 mg/dl) obscured the effects of these two sulfonylureas on CH2O. Thiazide or ethacrynic acid enhancement of chlorpropamide antidiuresis was also blunted by hyperglycemia and attendant osmotic diuresis. Thus, the low incidence of symptomatic hyponatremia during chlorpropamide treatment of diabetic patients may be explained by persistent hyperglycemia in such patients.

Radioimmunoassay of vasopressin in familial cental diabetes insipidus

We examined plasma arginine-vasopressin concentrations by radioimmunoassay in two brothers, aged 6 and 7.5 years, with familial central diabetes insipidus inherited as an autosomal dominant trait. Plasma AVP was measured in relation to increasing plasma osmolality induced by water deprivation and hypertonic saline infusion. The brother with the more severe urinary concentrating defect had no detectable AVP when his plasma osmolality was as high as 306 mOsm/kg; the other brother had detectable but clearly subnormal AVP concentrations. The one brother tested had an apparently normal end-organ response to exogenous vasopressin. Chlorpropamide had a significant antidiuretic effect in the brother with detectable AVP levels, and a lesser effect in the other brother . Our findings suggest that intrafamilial variation in the severity of congenital DI is related to the degree of vasopressin deficiency.

Water metabolism in diabetes mellitus

Transcellular shifts of water and changes in the physiology of water excretion are common in diabetes mellitus and its treatment. Recent evidence indicates that hyperglycemia in diabetic patients, but not in normal subjects, is characterized by elevations of circulating levels of arginine vasopressin (AVP; antidiuretic hormone, ADH). The role and importance of these observations remain to be defined since elevations of plasma AVP levels do not decrease water excretion in diabetic patients. Certain oral sulfonylureas, notably chlorpropamide and tolbutamide, are known to decrease renal free water clearance (CH2O), whereas insulin increases CH2O; the insulin and tolbutamide effects may be clinically trivial, whereas that of chlorpropamide is important. The hyponatremic effect of chlorpropamide may be exaggerated in diabetic patients by concomitant diuretic therapy. Euglycemia during chlorpropamide therapy appears to allow full expression of the action of chlorpropamide on CH2O; hyperglycemia with attendant osmotic diuresis protects chlorpropamide-treated patients against hyponatremia. Inhibition of prostaglandin synthesis with nonsteroidal anti-inflammatory agents enhances expression of the ADH effect on the kidney, but it does not appear to potentiate chlorpropamide hyponatremia. Two other oral sulfonylurea agents, tolazamide and glyburide, increase CH2O. Diazoxide is an antihypertensive thiazide which is antidiuretic as well as hyperglycemic. Thus, abnormalities of water metabolism are common in diabetes mellitus. Whether certain of these abnormalities are clinically important depends upon the presence of the osmotic diuresis of hyperglycemia and the pharmacology of diabetic management.

Chlorpropamide effect: measurement of neurophysin and vasopressin in humans and rats

The effect of chlorpropamide on neurohypophyseal function was studied by measurement of neurophysin and vasopressin in humans and in rats. Administration of chlorpropamide was shown to inhibit the ability of the human subjects and of the rats to maximally dilute their urine after administration of water. Comparison of the levels of vasopressin and neurophysin before and after the administration of chlorpropamide in the basal state and after water loading in both the human subjects and in rats showed no lack of suppression due to the chlorpropamide. The levels of both peptides were measured at the limits of detection. In other studies where neurophysin and vasopressin were readily detected, administration of chlorpropamide did not result in any augmented release of neurophysin or vasopressin in response to stimulation of the neurohypophysis in humans nor in rats. Levels of neurophysin in the pituitaries of rats showed no change in rats given chlorpropamide, while the content of vasopressin was increased, possibly indicating a chronic decreased secretion of vasopressin in rats given chlorpropamide.

Oral hypoglycemic agent update

The treatment of diabetes is still a problem more than a half-century after the discovery of insulin. Patients are now living significantly longer but until the development of oral hypoglycemic agents, the only direct treatment modalities were exercise, diet, and insulin. Before evaluating the effectiveness of treatment, a therapeutic goal must be determined. While there are no absolutely "hard" facts proving that "good control" is beneficial in preventing chronic complications of diabetes, increasing accumulation of "soft" data strongly suggests that normal blood glucose levels are most desirable, when possible, but not at the cost of severe or disabling hypoglycemic reactions. The development of the oral agents was a great public health advance in that many persons with early diabetes, but fearful of insulin injections, had less dread of "the pills" and sought treatment. The oral agents simplified care but this very simplification process often undermined the need for proper diet and good fundamental care. This often led to mediocre diabetes care. While useful, the oral agents have marked limitations and in some are effective only temporarily. The presently available oral agents are sulfonylureas and require a viable beta-cell system for success. This limits the number of diabetics responsive to such treatment. The general indications for tolbutamide, chlorpropamide, acetohexamide and tolazamide are in maturity-onset diabetics, generally beyond the age of 40 with diabetes of less than 10 years. They are contraindicated in juvenile-onset diabetics, in pregnant women, and usually in patients undergoing major surgery, and can become ineffective during periods of extreme stress or during severe infection. They can lower blood glucose levels if used in proper doses in properly selected patients. Contrary to several decades of documentation, it has become popular to suggest that the oral agents are not effective. They can be effective but for many reasons apparently were not in their use by the U.G.D.P. researchers. This might not be the fault of the oral agent used. If ineffective, they should be discontinued. Many, but not all, patients may respond to diet therapy, which is then the treatment of choice. Obviously insulin, though difficult to use for many persons and in itself able to induce several severe reactions if not used properly, is the only treatment (with diet) for the severe diabetic. There is a large spectrum of patients inbetween in whom the oral agents may be useful. The use of phenformin (phenethyl-biguanide) has been effectively curtailed because of many reported cases of lactic acidosis, and while it is doubtful that phenformin alone, in the absence of complicating factors, is the causative factor, it is capable of being an augmenting influence when other conditions, such as decreased kidney function, prevail...

Water metabolism

Total body water is finely regulated and controls of intake and output are maximally activated by small osmotic changes. Sensors in the hypothalamus invoke the fluid repletion or depletion reactions through changes in thirst, urine concentration and solute intake. Antidiuretic hormone controls urinary concentration and is released mainly in response to osmotic stimuli. However, the threshold and sensitivity of this response are affected by non osmotic stimuli. Urine concentration varies in response to antidiuretic hormone only if the distal tubule, collecting duct and hypertonic medullary interstitum are intact. The capacity to conserve or excrete water depends on the osmolar load and an efficient urinary concentrating or diluting mechanism.

Disorders of thirst are uncommon and often associated with abnormal antidiuretic hormone secretion. Disorders of urine concentration and dilution are common in illness and reflect abnormalities of antidiuretic hormone secretion or the renal mechanisms generating the osmotic gradient. When urine concentrating capacity is impaired ( true or nephrogenic diabetes insipidus) water depletion occurs only when thirst fails or access to water is denied. When urine diluting ability is impaired, water excess occurs when the osmolar load and minimum urinary osmolality generated are inadequate for the fluid intake.

Hyper-osmolality and hypo-osmolality are usually caused by abnormal water metabolism although they may be associated with abnormalities of solute metabolism. The various clinical syndromes are determined by the primary disease, and the associated fluid volume and osmolar abnormalities.

Inappropriate secretion of antidiuretic hormone. An overview of the syndrome

The syndrome of inappropriate secretion of antidiuretic hormone is characterized by production of less than maximally dilute urine in the presence of hypotonic plasma. It may be secondary to malignant disease, central nervous system disorders, or pulmonary disease, among other conditions, or it may be idiopathic. Manifestations are those of water intoxication, eg, confusion, fatigue, nausea, headache, and neurologic signs. The pathogenesis is not completely understood. Restriction of fluid intake to obtain a negative water balance is effective treatment.

Comparison of clofibrate and chlorpropamide in vasopressin-responsive diabetes insipidus

Six patients with vasopressin-responsive diabetes insipidus (DI) received clofibrate and chlorpropamide, singly and in combination. Decrease in urinary output averaged (mean +/- SEM): (1) clofibrate 2 g/day, 47% +/- 6%; (2) chlorpropamide 250 mg/day 59% +/- 5%; (3) clofibrate 2 g/day plus chlorpropamide 125 mg/day, 54% +/- 7%; (4) clofibrate 2 g/day plus chlorpropamide 250 mg/day 61% +/- 4%. Water deprivation tests before and during treatment showed significantly higher basal, final, and peak urinary osmolalities (Uosm) and lower free water clearance (CH20) on chlorpropamide, singly and in combination: clofibrate raised Uosm less but significantly decreased CH2O. Water load tests before and during treatment showed that chlorpropamide, singly and in combination, markedly decreased maximal urinary flow, maximal CH2O, percentage water load excreted, and increased minimal Uosm; clofibrate significantly decreased maximal urinary flow and CH2O only. One patient responded only to combination therapy. Chlorporpamide caused serious hypoglycemia in three of six patients. Clofibrate had no significant side effects.

Symptomatic hyponatraemia associated with tolbutamide therapy

A case of hyponatraemic coma occurring in a patient with diabetes mellitus treated with tolbutamide is described. Although chlorpropamide is known to cause water retention in some circumstances, this is a less well recognized complication of tolbutamide therapy.

Juvenile diabetes mellitus, optic atrophy, hearing loss, diabetes insipidus, atonia of the urinary tract and bladder, and other abnormalities (Wolfram syndrome). A review of 88 cases from the literature with personal observations on 3 new patients

A review of 88 cases from the literature with personal observations on 3 new patients is given of the syndrome featured by juvenile diabetes mellitus, optic atrophy, hearing loss, diabetes insipidus, atonia of the urinary tract and bladder and other abnormalities. The postmortem in one of our cases is mentioned. The pattern of inheritance is autosomal recessive. The interpretation of the data on diabetes insipidus from the literature and in our three patients is also discussed. It can only be stated that neurohypophyseal diabetes insipidus can be a component of the syndrome and that in many cases--particularly in the presence of lesions of the efferent urinary tract--the possibility of nephrogenous diabetes insipidus can not be excluded with certainty. It seems probable that the same mechanism can be held responsible for the lesions of the olfactory, optic, vestibular and cochlear nerves, the hypophyseal form of diabetes insipidus, retarded sexual maturation, abnormal pupillary reaction, myelopathy and the electro-encephalographic, electroneurological and electromyographic changes in the Wolfram syndrome. The process underlying this affection of neural structures remains obscure.

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

SIADH consists of hyponatremia and hyposmolality, continued urinary loss of sodium, excretion of an inappropriately concentrated urine, and absence of dehydration, usually in the presence of normal renal and adrenal function. The retention of excess water caused by the inappropriate secretion of antidiuretic hormone is central to the development of the syndrome. In pediatrics, SIADH is most commonly seen in patients with meningitis or postoperatively. Fluid restriction is vital in such patients to prevent the development of symptomatic SIADH. Fluid restriction alone will also result in the correction of serum electrolyte composition in patients with SIADH. Hypertonic saline should be used only in severely symptomatic patients.

Pathophysiologic and pharmacologic alterations in the release and action of ADH

The physiologic factors involved in vaseopressin (ADH) release and action are reviewed with emphasis on the interaction between osmotic and volume stimuli to the discharge of ADH. Abnormalities in reception of stimuli to ADH release, and in the impaired synthesis and release of ADH, are reviewed in relation to the causes of diabetes insipidus, and information on the biochemical changes which have been described in patients with nephrogenic diabetes insipidus is also discussed. We summarize the pathologic lesions and associated diseases found in 54 of our patients with diabetes insipidus. Criteria for establishing the diagnosis of diabetes insipdus are reviewed with emphasis on the dehydration test, including the importance of measuring plasma osmolality at the conclusion of water deprivation. Treatment of diabetes insipidus is briefly discussed with emphasis on the use of DDAVP and oral agents. The syndrome of inappropriate ADH secretion (SIADH) is reviewed including our experience with 39 patients. The differential diagnosis of SIADH, including the value of water loading and the measurement of ADH levels, is discussed. We comment on treatment of these patients including the use of investigational drugs. Lastly, we review the pharmacologic features and clinical relevance of some drugs which alter the release and action of ADH.

DDAVP in the treatment of central diabetes insipidus

DDAVP, 1-desamino-8-d-arginine-vasopressin, is a synthetic analogue of vasopressin with increased antidiuretic activity and decreased pressor activity. Whereas the antidiuretic-to-pressor ratio of arginine vasopressin is 1, the antidiuretic-to-pressor ratio of DDAVP is 4000. When administered as an intranasal spray, 5 to 20 mug of DDAVP produced eight to 20 hours of antidiuresis in patients with complete central diabetes insipidus. The minimum recommended therapeutic dose resulted in a maximum antidiuresis in most patients. No side effects of the drug were noted in clinical trials. DDAVP thus gives promise of becoming the standard treatment of severe central diabetes insipidus.

The effect of chlorpropamide on water balance in pitressin-treated Brattleboro rats

1 The daily administration of a 5% glucose solution to the heterozygous Brattleboro rat produced an experimental model in a comparable state of polydipsia and polyuria to the homozygous rat with diabetes insipidus (DI).2 The effect of chlorpropamide on water metabolism was then examined in both the homozygous DI rat treated with submaximal doses of pitressin tannate in oil (Pitressin), and in the glucose-hydrated heterozygous rat with and without simultaneous pitressin therapy.3 A dose-response curve for chlorpropamide (5, 10, and 20 mg/24 h) in DI rats treated with Pitressin (25 mu/24 h) indicated that the drug decreased fluid intake further, but only by a maximum of 13.8% (at the 20 mg/24 h dose of chlorpropamide), differing markedly from results obtained in patients with diabetes insipidus. A second experiment in which chlorpropamide (5 mg/24 h) was administered to DI rats treated with Pitressin (either 25 or 50 mu/24 h) confirmed the lack of any significant drug-effect on water metabolism in these animals.4 Chlorpropamide (20 mg/24 h), when administered alone or simultaneously with a submaximal dose of Pitressin (25 mu/24 h), had no obvious effect on the fluid intake of glucose-hydrated heterozygous rats. The absence of any action by chlorpropamide on water metabolism was confirmed in these experimental animals using 5 mg/24 h of the drug together with Pitressin (either 25 or 50 mu/24 hours).5 Indirect evidence for the slower growth-rate in the DI rat being due to an insufficient daily calorific intake was obtained from the study on glucose-hydrated heterozygous rats.

Clofibrate-induced antidiuresis

Normal subjects and patients with antidiuretic hormone (ADH) deficiency were studied to determine the mechanism of the antidiuretic action of clofibrate. Before clofibrate treatment, the patients' ability to concentrate urine with a standardized dehydration procedure correlated with the amount of ADH which was excreted. During clofibrate administration all six patients with ADH deficiency developed an antidiuresis which was like that of ADH, since there was no change in sodium, potassium, total solute, or creatinine excretion. There was a correlation between the patients' ability to concentrate urine during dehydration and the subsequent response to clofibrate, and the excretion of ADH during dehydration correlated with the excretion of ADH on clofibrate therapy. Clofibrate-induced antidiuresis in these patients was partially overcome by ethanol and by water loading. Clofibrate interfered with the ability of patients and subjects to excrete a water load and prevented the water load from inhibiting ADH excretion in the normal subjects. These studies suggested that clofibrate was acting through endogenous ADH and this thesis was supported by the failure of clofibrate to produce an antidiuresis when injected into rats with total ADH deficiency (Brattleboro strain) although an antidiuresis was produced in water-loaded normal rats. When the drug was injected into Brattleboro rats with exogenous ADH, clofibrate either did not alter or it inhibited the action of the ADH. The data demonstrate that clofibrate has a significant ADH-like action. This action appears to be mediated through the release of endogenous ADH.