Gunther Schlager

Chronic hypertension and altered baroreflex responses in transgenic mice containing the human renin and human angiotensinogen genes.

We have generated a transgenic model consisting of both the human renin and human angiotensinogen genes to study further the role played by the renin-angiotensin system in regulating arterial pressure. Transgenic mice containing either gene alone were normotensive, whereas mice containing both genes were chronically hypertensive. Plasma renin activity and plasma angiotensin II levels were both markedly elevated in the double transgenic mice compared with either single transgenic or nontransgenic controls. The elevation in blood pressure caused by the human transgenes was independent of the genotype at the endogenous renin locus and was equal in mice homozygous for the Ren-1c allele or in mice containing one copy each of Ren-1c, Ren-1d, or Ren-2. Chronic overproduction of angiotensin II in the double transgenic mice resulted in a resetting of the baroreflex control of heart rate to a higher pressure without significantly changing the gain or sensitivity of the reflex. Moreover, this change was not due to the effects of elevated pressure itself since angiotensin-converting enzyme inhibition had minimal effects on the baroreflex in spontaneously hypertensive BPH-2 control mice, which exhibit non-renin-dependent hypertension. This double transgenic model should provide an excellent tool for further studies on the mechanisms of hypertension initiated by the renin-angiotensin system.

Natural mutation rates in the house mouse. Estimates for five specific loci and dominant mutations.

Abstract More than 7 million mice were examined for grossly visible spontaneous mutations. A total of 249 mutations were recovered, of which 206 could be characterized as their mode of inheritance (dominant or recessive). The rates of spontaneous mutations at 5 specific coat-color loci ( a , b , c , d , and ln ) were 11 · 10 −6 per locus per gamete for mutations from wild-type, and 2.5 · 10 −6 for mutations from recessive alleles. Large differences were found between the rates of the individual loci; the a , a + , and c + alleles had the highest rates. Estimates of “forward” and “reverse” mutations at each of these five loci also showed large differences. A comparison of the rates at the five specific loci and those at other loci for which dominant mutations were recovered showed that the specific loci used in this study had a spontaneous mutation rate 6 times higher. No effect of the age of parent was discernible for those loci where sufficient numbers of mutants were recovered to make a meaningful comparison.

Consumption of electrolytes and quinine by mouse strains with different blood pressures

Daily fluid intakes were measured using two-bottle tests in female mice of inbred strains with high (BPH/2), normal (BPN/3) or low (BPL/1) blood pressure. The mice were offered a choice between water and different concentrations of NaCl (37.5-600 mM), KCl (1-400 mM), CaCl2 (1-100 mM) and quinine hydrochloride (0.003-1.0 mM). Compared with the normotensive strain, the hypertensive mice had higher water and total fluid intakes, and lower intakes of NaCl, KCl (only 200 mM) and quinine; the hypotensive mice had higher intakes of KCl (only 10-50 mM) and lower intakes of CaCl2 and quinine. These data suggest that fluid and salt intake are not linearly related to blood pressure, but are independently determined in these strains. Certain concentrations of the salts were preferred relative to water, which depended on mouse genotype: the BPN/3 and BPL/1 mice strongly preferred 37.5-150 mM NaCl, the BPL/1 mice preferred 10-100 mM KCl, and the BPN/3 mice preferred 1-10 mM CaCl2.

Biometrical Genetic Analysis of Blood Pressure Level in the Genetically Hypertensive Mouse

Hypertensive mice of the inbred strain BPH/2 were mated to mice of the inbred hypotensive BPL/1, and their hybrid offspring were crossed and intercrossed. The systolic blood pressures of the resulting ten populations were then subjected to a biometrical genetic analysis to determine the mode of inheritance of genes regulating blood pressure in these strains. It was found that the inheritance of elevated blood pressure was due, primarily, to the additive effects of three to five genes. There was no evidence that genetic dominance or epistasis were involved in the genetic control of blood pressure in these strains.

Urinary kallikrein and urinary prostaglandin E2 in genetically hypertensive mice.

Summary We have evaluated urinary kallikrein activity and urinary prostaglandin E2 (PGE2) immunoreactivity in Schlager high blood pressure (HBP) and low blood pressure (LBP) mice. Urinary kallikrein activity was measured by a colorimetric method employing α-N-p-tosyl-L-arginine methyl ester HCl (TAME) as substrate. It was shown that urinary TAME esterase activity in HBP and LBP mice was probably due to a single enzyme and that this enzyme appeared to be urinary kallikrein. Urinary PGE2 immunoreactivity was determined by a specific radioimmunoassay. Urinary kallikrein activity was significantly elevated and urinary PGE2 immunoreactivity was significantly reduced in HBP compared to LBP mice. High urinary kallikrein activity in HBP mice resembles situations such as human primary aldosteronism, where hypertension is produced by mineralocorticoid excess. Low urinary PGE2 levels in HBP mice, however, compares to the situation observed for human essential hypertension. The HBP mouse thus has alterations in physiological parameters believed to reflect renal blood pressure regulating mechanisms. These alterations are unique among genetically hypertensive animal models and appear to be analogous to alterations seen in certain human hypertensive states. One possible explanation for the inverse relationship between urinary kallikrein activity and urinary PGE2 levels in HBP and LBP mice is that HBP mice could have a physiological block preventing stimulation of renal prostaglandin synthesis by the renal kallikrein-kinin system. We are indebted to D. W. Sandwisch for his very helpful technical advice and to P. K. Howell for her technical assistance.

Catecholamine concentrations in discrete brain nuclei and sympathetic tissues of genetically hypertensive mice.

Catecholamine concentrations were determined at central and peripheral level in high blood pressure (HBP), low blood pressure (LBP) and random bred (RB) mice. In HBP mice compared to LBP, the noradrenaline concentration was lower in the locus coeruleus, medullary A1-C1 and A2-C2 areas, thoracic spinal cord, posteroventral hypothalamus and nucleus hypothalamicus anterior, while dopamine concentration was decreased in the striatum. Adrenal catecholamine levels were higher in both HBP and LBP compared to RB mice.

Aggressive social interaction in mice genetically selected for blood pressure extremes.

Mice genetically selected for blood pressure extremes were compared with regard to aggressive social behavior. Aggressor mice from the high and low blood-pressure lines were pitted against mice from the high and low lines (targets). High blood-pressure mice were less aggressive socially than low blood-pressure mice. The low blood-pressure mice exhibited the highest social aggression scores when pitted against high blood-pressure targets. Examination of extreme blood-pressure groups chosen from the segregating F 2 generation resulting from crosses of the high and low lines indicated that aggressive social behavior and blood pressure were influenced by the same genes or linked genes.

Spontaneous mutation rates at five coat-color loci in mice.

Examination of 1.5 million mice yielded natural mutation rates estimnated from 5.2 million gene reproductions at five specific coat-color loci. The average rates were 11.1 x 10-6 for forward mutations and 2.7 x 10-6 for reverse mutations. Differences between the frequencies of mutations at the individual loci were evident.

Abnormality of calmodulin activity in hypertension. Evidence of the presence of an activator.

An apparent increase of calmodulin (CaM) activity was previously observed in the heart and kidney but not in the liver of spontaneously-hypertensive rats (SHR) and mice compared with their corresponding normotensive controls. As this change was due to an elevated recovery of CaM in the organs of the hypertensive animals, the present study was designed to evaluate its activity in hypertension. A CaM activator, detected in heart and kidney supernatants from hypertensive animals, was found to be responsible for this enhanced recovery. Similar results were obtained with passaged, cultured aortic smooth muscle cells from SHR, indicating that the anomaly was not a mere consequence of elevated blood pressure but rather a genetic expression of cells of hypertensive origin. The activator was heat stable, nondialyzable, and recovered in the fraction precipitated with 30-50% ammonium sulfate. Preliminary extraction studies suggest that the activator is contained in a glycolipid fraction. The stimulation of phosphodiesterase by this activator was calcium and CaM dependent. The activator appears to affect the affinity of the phosphodiesterase for CaM rather than the maximal stimulation. The activator was also present at a low concentration in the heart and kidney of normotensive animals. These findings indicate that at least some of the calcium abnormalities implicated in the pathogenesis of hypertension could be the result of interactions between CaM, calcium, and this activator.

Natural mutation rates in the house mouse: Plan of study and preliminary estimates

Abstract From the autumn of 1963 to the summer of 1964, 630320 mice in 18 inbred strains and 173754 mice in six F 1 hybrid generations, produced under regular laboratory conditions, were examined for presumptive natural mutations at any one of five specific coat color loci and at any other locus as well. Altogether 40 of 303 presumptive mutations have proved to be mutations. The preliminary estimates of reverse (recessive to dominant) mutation rates are: 6.5·10 −6 for nonagouti ( a ) to alleles a t adn A w ; 3.6·10 −6 for dilution ( d ) to wild type ( d + ); o for the brown ( b ), albino ( c ), and leaden ( ln ) loci. The preliminary estimates of forward (dominant to recessive) mutation rates range up to 30·10 −6 for the ln locus. Other estimates are 1.1·10 −6 for the tabby ( Ta ) locus and 4.9·.10 −6 for the dominant spotting ( W ) locus. The occurrence of gonadal mosaics may eventually be a means of studying the mutability of genes in cells at all stages of development.