Age-related changes in body fluid volumes in young spontaneously hypertensive rats

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Impact of Fenugreek on Milk Production in Rodent Models of Lactation Challenge

Fenugreek, a herbal remedy, has long been used as galactologue to help mothers likely to stop breastfeeding because of perceived insufficient milk production. However, few studies highlight the efficacy of fenugreek in enhancing milk production. The aims of our study were to determine whether fenugreek increased milk yield in rodent models of lactation challenge and if so, to verify the lack of adverse effects on dam and offspring metabolism. Two lactation challenges were tested: increased litter size to 12 pups in dams fed a 20% protein diet and perinatal restriction to an 8% protein diet with eight pups’ litter, with or without 1 g.kg⁻¹.day⁻¹ dietary supplementation of fenugreek, compared to control dams fed 20% protein diet with eight pups’ litters. Milk flow was measured by the deuterium oxide enrichment method, and milk composition was assessed. Lipid and glucose metabolism parameters were assessed in dam and offspring plasmas. Fenugreek increased milk production by 16% in the litter size increase challenge, resulting in an 11% increase in pup growth without deleterious effect on dam-litter metabolism. Fenugreek had no effect in the maternal protein restriction challenge. These results suggest a galactologue effect of fenugreek when mothers have no physiological difficulties in producing milk.

Operant self-administration of sweetened ethanol and time course of blood ethanol levels in adolescent and adult male Long-Evans rats

BACKGROUND

Little is known regarding mechanisms regulating ethanol (EtOH) self-administration during adolescence or if the mechanisms differ from adults. One of the best models of abuse liability is operant self-administration. Therefore, we characterized operant sweetened EtOH self-administration behavior in adolescent and adult rats.

METHODS

Adolescent (36 days old at first EtOH exposure) and adult male Long-Evans rats were first trained to self-administer 10% sucrose (10S) in an appetitive/consummatory operant model for 1 week, and then the drinking solution was switched to 10% sucrose plus 10% EtOH (10S10E) for 2 weeks. Next, rats were switched to a fixed ratio 2 schedule, and this was followed by 1 session using a progressive ratio schedule of reinforcement. Last, rats were tested for cue-induced reinstatement of lever-pressing behavior under extinction conditions after 13 days of abstinence. Blood EtOH concentration (BEC) of sweetened EtOH (self-administered or intragastric [IG] administration of 1 g/kg) was determined via gas chromatography. Control rats drank only 10S.

RESULTS

Consumption of sweetened EtOH was not different between adolescents and adults under any schedule tested, reaching 1 g/kg in 20 minutes in the appetitive/consummatory model. Appetitive behavior directed at sweetened EtOH was less focused in adolescents versus adults. No age differences were found in motivation for sweetened EtOH. Cue-induced reinstatement of EtOH-seeking behavior after abstinence also did not differ by age. In control groups, no age difference was found in appetitive behavior or the amount of sucrose consumed, although adults exhibited greater cue-induced reinstatement. BEC after self-administration or IG administration of sweetened EtOH was higher in adults than adolescents.

CONCLUSIONS

Consumption and motivation for sweetened EtOH are similar in adolescents and adults, although adolescents are more vulnerable to the effects of EtOH consumption on appetitive behavior. The IG results suggest larger volume of distribution and higher first-pass metabolism of sweetened EtOH in adolescents versus adults, which may limit the reinforcing effects of EtOH in some adolescents. Overall, we have begun to establish an operant sweetened EtOH self-administration model in adolescent rats.

Analysis of arterial pressure regulating systems in renal post-transplantation hypertension

OBJECTIVE

To investigate if blood volume expansion, increased sodium retention, changes in neurohumoral arterial pressure control, or altered extrarenal resistance vessel function contribute to the development of renal post-transplantation hypertension.

METHODS

F1-hybrids (F1H) obtained from crossing spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats received either an SHR or an F1H kidney graft. Groups consisted of 8-12 animals and were investigated between days 1 and 14 after renal transplantation in three sets of experiments including arterial pressure recordings, plasma volume measurements, metabolic studies, and small vessel myography.

RESULTS

Two days after completion of bilateral nephrectomy, arterial pressure was elevated by 15-20 mmHg in recipients of an SHR kidney, compared with syngeneically transplanted controls. There was no evidence for increased sodium and fluid retention during the early development of renal post-transplantation hypertension despite a 35% reduced creatinine clearance in recipients of an SHR kidney. The plasma renin-angiotensin-aldosterone system was similarly suppressed in both recipients of an SHR kidney and controls. The arterial pressure response to ganglionic blockade did not differ between groups and there was no evidence for changes in extrarenal resistance vessel function, which could be involved in the genesis of this form of hypertension.

CONCLUSIONS

None of the investigated mechanisms was altered in a way that might help to explain the rapid and consistent development of hypertension in recipients of an SHR kidney. We conclude that post-transplantation hypertension in recipients of an SHR kidney is due to mechanisms other than those investigated in the present study.

Proximal tubule Na transporter responses are the same during acute and chronic hypertension

Acute hypertension in Sprague-Dawley rats (SD) provokes a decrease in renal proximal tubule (PT) salt and fluid reabsorption, redistribution of apical Na/H exchanger isoform 3 (NHE3) and Na-P(i) cotransporter type 2 (NaPi2) out of the brush border into higher density membranes, and inhibition of renal cortical Na-K-ATPase (NKA) activity (41). The aims of this study were to determine 1) whether an increase in arterial pressure affects distribution or activity of Na transporters in the spontaneously hypertensive rat (SHR) and 2) whether development of chronic hypertension in SHR leads to persistent adaptive changes in NHE3 and NaPi2 distribution and/or NKA activity. Renal cortex Na transporter protein density distributions and activities were compared by subcellular fractionation in 1) adult SHR with an acute increase or decrease in arterial pressure and 2) young SD (YSD) and young SHR (YSHR) vs. adult SD and SHR. In adult hypertensive SHR NHE3 was shifted to membranes of higher densities, analogous to SD with acute hypertension, and there were no further changes with a further increase or decrease in arterial pressure. There was no change in total pool size of NHE3 in cortex in YSHR vs. SHR. NHE3, NaPi2, megalin, NKA alpha-/beta-subunit, dipeptidyl peptidase IV (DPPIV), and villin distributions were the same in YSHR vs. YSD. NHE3, NaPi2, and megalin shifted to higher densities in adult SHR, but not SD, with age. Basolateral NKA and apical alkaline phosphatase activities were 40% greater in YSHR than YSD and decreased to SD levels in adults. We conclude that there are persistent changes in Na(+) transporter distributions and activity in response to chronic hypertension in SHR that mimic the responses to acute hypertension seen in SD rats and that elevated sodium pump activity per transporter in YSHR may contribute to the generation of hypertension.