Chronic manipulation of dietary salt modulates renal physiology and kidney dopamine receptor subtypes: functional and autoradiographic studies.

1. Compared to rats maintained on the normal NaCl (0.33%) diet, animals maintained on the low NaCl (0%) diet for 4 weeks exhibited increased plasma aldosterone and chloride and decreased urinary sodium excretion. 2. Rats maintained on the high NaCl (8%) diet for 4 weeks showed increased systolic blood pressure, water intake, urine volume, sodium and dopamine excretion and decreased plasma aldosterone and glomerular filtration rate. 3. Administration of SCH 23390 (10 mg/kg, po), but not domperidone to the high salt diet rats attenuated the diuretic effect, indicating the involvement of DA1 rather than DA2 receptors. The dopamine decarboxylase inhibitor, carbidopa (30 mg/kg, i.p.), also reduced the high salt-induced diuresis. 4. Kidney sections from rats fed the low NaCl diet showed a 63-100% decrease (P < 0.001-0.02) in cortical and medullary DA1 and DA2 binding sites, while rats fed the high NaCl diet demonstrated only a 70% decrease (P < 0.01-0.02) in cortical DA1 binding, without affecting DA2 binding. 5. These data indicate that chronic modification of dietary salt profoundly affects the sodium, water and dopamine excretion and leads to selective modulation of renal dopamine receptor subtypes.

Quantitative autoradiography demonstrates selective modulation of rat brain regional dopamine (D1 and D2) receptor subtypes after chronic manipulation of dietary salt.

The effects of chronic dietary sodium chloride (NaCl) consumption on renal function and brain dopamine receptors were studied in adult, male normotensive rats. Compared to rats maintained on the normal NaCl (0.33%) diet, animals maintained on the low NaCl (0%) diet for 4 weeks exhibited significant increases in plasma aldosterone, chloride and changes in urinary electrolyte excretion. In contrast, rats maintained on the high NaCl (8%) diet for 4 weeks demonstrated significant increases in urine volume and urinary sodium, chloride and dopamine excretions and water intake. Rats fed the high NaCl diet displayed a 42-59% decrease (p < 0.001-0.05) in D1 binding in the nucleus accumbens (NA), olfactory tubercle (OT) and the striatum (STM), without any effects on D2 binding in these brain regions. Rats maintained on the low NaCl diet also demonstrated decreased D1 binding in the ventral (24%, p < 0.02) and lateral (29%, p < 0.01) STM, but not in the OT, NA, entopeduncular nucleus and substantia nigra. Rats fed low or high NaCl diets exhibited a 35-180% increase (p < 0.01-0.05) in D2 binding in several mid-brain areas (e.g. hypothalamus, thalamus and hippocampus) and hindbrain regions (e.g. superior colliculus and nucleus tractus solitarius) without affecting the D1 binding. These data indicate that chronic modification of dietary salt intake profoundly affects the renal handling of sodium/water excretion and leads to selective up- and/or down-regulation of DA receptor subtypes in different areas of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

A pharmacological comparison of [3H]GBR12935 binding to rodent striatal and kidney homogenates: binding to dopamine transporters?

Binding of [3H]GBR12935 to homogenates of mouse and rat striatum and kidney was studied. [3H]GBR12935 bound to both tissue preparations with high affinity (mouse striatum Kd = 2.4 +/- 0.4 nM, n = 4; mouse kidney Kd = 3.8 +/- 0.9 nM, n = 4), in a saturable (striatal Bmax = 1.5 +/- 0.4 pmol/mg protein; kidney Bmax = 4.9 +/- 0.5 pmol/mg protein) and reversible manner. Saturation experiments revealed the presence of a single class of high affinity binding sites in both tissues of both species. Mouse kidney appeared to possess a greater density of [3H]GBR12935 binding sites than the striatum while the reverse situation prevailed for the rat. Although two dopamine uptake inhibitors, namely GBR12909 and benztropine, displaced [3H]GBR12935 binding from striatal and kidney homogenates with a similar affinity in both tissues of these species, unlabelled mazindol, (+/-)cocaine, nomifensine and amfonelic acid were significantly (P < 0.001-0.02) more potent inhibitors of [3H]GBR12935 binding in the striatum than in the kidney. While the pharmacological profile of [3H]GBR12935 binding in the rodent striatum compared well with that of the dopamine transporter reported previously, the pharmacology in the kidney was considerably different to that in the striatum. GBR12909 (1-30 mg/kg, i.p.), a close analog of GBR12935, induced significant antidiuretic and antinatriuretic effects in spontaneously hypertensive rats. These data suggest that while [3H]GBR12935 labels the dopamine uptake sites in the brain, it does not appear to label similar sites in the kidney. The mechanism of action of GBR12909 on sodium and water excretion remains to be determined.

Renin and angiotensinogen expression during the evolution of diabetes.

The expression of renin and angiotensinogen genes and their proteins were studied during the progression of diabetes using adult BioBreeding spontaneously diabetic rats at 1 day and 2-12 months of diabetes. The number of renin-stained cells per juxtaglomerular apparatus was determined by immunocytochemistry. Initially, at 2 months of diabetes the number of renin-stained cells per juxtaglomerular apparatus increased significantly (p less than 0.0001, 2 months versus resistant groups) and was followed by a decrease in the number and intensity of renin-stained cells after 12 months of diabetes (p = 0.007, 2 months versus 12 months). A significant negative correlation was observed between the number of renin-containing cells and the duration of diabetes (r = 0.99, p = 0.014). Immunoreactive angiotensinogen was restricted to the proximal tubule and appeared increased after 4 and 8 months of diabetes as compared with the 2- and 12-month diabetic groups. Renin messenger RNA (mRNA) levels increased with the onset of diabetes and decreased markedly during chronic diabetes. At 1 day of diabetes, renin mRNA levels were 700% higher than at 12 months of diabetes. Angiotensinogen mRNA levels were unchanged. We conclude that diabetes results in an initial increase in renin gene expression, and as the duration of diabetes lengthens, there is a progressive decrease in renin gene expression and in the number of cells containing renin. These findings suggest that as the duration of diabetes and the age of the animal lengthens, there is a decrease in the number of cells expressing the renin gene.

Effects of the natural and unnatural isomers and degradation products of enprostil on gastric acid secretion and gastrointestinal motility in the rat.

The gastric antisecretory and gastrointestinal (GI) motility activity of the natural and unnatural allenic isomers and degradation products of enprostil (methyl(+/-)-7-[(1R*,2R*,3R*)-3-hydroxy-2-[(E)-(3R*)-3-hydroxy-4-phenoxy - 1-butenyl]-5-oxocyclopentyl]-4,5-heptadienoate, RS-84135-004) were studied in the rat. The natural R-allenic isomer of enprostil was the most potent antisecretory compound. The 8-iso-enprostil, enprostil free acid, and the 5-acetylene isomer had somewhat less activity while the other compounds were relatively inactive. The natural and unnatural allenic isomers increased intestinal dye transit with the same rank potency as the gastric antisecretory activity. Enprostil, 8-iso-enprostil, prostaglandin A-enprostil and enprostil free acid, all increased intestinal dye transit.

Effects of enprostil on cardiovascular and respiratory parameters in the dog, and on hematologic parameters in the rat, monkey, and human.

The effects of enprostil (+/-)-7-[(1R*,2R*,3R*)-3-hydroxy-2-[(E)-(3R*)-3-hydroxy-4-phenoxy-1- butenyl]-5-oxocyclopentyl]-4,5-heptadienoate) were studied on cardiovascular and respiratory parameters in the dog and on hematologic parameters in the rat, monkey, and human. Anesthetized dogs were instrumented to allow measurement of heart rate, systemic blood pressure, respiratory rate or tracheal pressure, and ventricular contractile force after intragastric (i.g.) or intravenous (i.v.) administration of enprostil in the presence or absence of autonomic challenges. The effects of intraduodenal (i.d.) enprostil on arterial and venous PO2, PCO2, and pH; respiratory rate, flow rate, and volume; blood pressure (b.p.); and heart rate were also examined. Enprostil i.v. (0.3-10 micrograms/kg) significantly increased tracheal pressure in a dose-dependent manner, but minimally altered b.p., heart rate, and ventricular contractile force. Enprostil i.v. (1-10 micrograms/kg) significantly inhibited pressor and depressor responses to several autonomic challenge agents at the highest dose level, indicative of a nonspecific inhibitory effect on b.p. responses. Cardiovascular effects of enprostil (1-100 micrograms/kg i.g.) were absent. Enprostil (10-3,000 micrograms/kg i.d.) had no noteworthy effects on respiratory parameters in the dog. Platelet aggregation effects of enprostil were studied in vitro using platelet rich plasma (PRP) from the rat, monkey, and human; whole blood clotting time and prothrombin time after oral enprostil were studied in the rat; and ex vivo effects on platelet activation were studied in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

[(1H-imidazol-1-yl)methyl]- and [(3-pyridinyl)methyl]pyrroles as thromboxane synthetase inhibitors.

Several [(1H-imidazol-1-yl)methyl]- and [(3-pyridinyl)methyl] pyrroles were prepared and evaluated in vitro as thromboxane synthetase inhibitors in human platelet aggregation studies. A number of structures, e.g. 10b,f,g,i (respective IC50 values: 1 microM, 50 nM, 42 nM, 44 nM) showed superior in vitro inhibition of TXA2 synthetase when compared to the standard dazoxiben (1). However, it was found that in vitro potency did not translate into nor correlate with in vivo activity when these compounds were evaluated in mice in a collagen-epinephrine-induced pulmonary thromboembolism model. (E)-1-Methyl-2-[(1H-imidazol-1-yl)methyl]-5-(2-carboxyprop-1-enyl) pyrrole (10b) was found to offer protection against collagen-epinephrine-induced mortality in mice, thereby demonstrating that oral administration is an effective route for absorption of this drug. Additional evidence for the oral effectiveness of 10b in lowering serum TXB2 levels was obtained by performing ex vivo radioimmunoassay experiments with rats. A 13-week study of 10b in rats with reduced renal mass was conducted in order to evaluate the role of TXA2 production in hypertension and renal dysfunction. Although serum and urinary TXB2 levels in rats were found to be lowered during this study by 10b, the levels of urinary protein excretion remained comparable to that of the control group.

Synthesis and pharmacological evaluation of N,N-di-n-propyldopamine congeners containing phenolic bioisosteres.

A series of analogues of N,N-di-n-propyldopamine (DPDA) in which the 3-hydroxyl group was replaced by bioisosteric groups was prepared and evaluated for D1- and D2-receptor affinity. The 3-methane-sulfonamide analogue (18) had a higher affinity for the D2 receptor than DPDA and was more selective for the D2 receptor. The 3-formamide derivative (15) also retained significant D2 affinity. Both of these compounds demonstrated in vivo cardiovascular and renal profiles in an anesthetized rat model that were consistent with selective D2-receptor agonism.