Transgenic rats: new animal models in hypertension research. Invited lecture.

Abstract

T he challenge in hypertension research is the elucidation of the primary genetic causes of elevated blood pressure. It is common knowledge that the basic information on how a cell, an organ, and the whole body function resides within the chromosomes and the individual genes, that is, their nucleotide DNA sequence. The problem with understanding primary (genetic) hypertension in humans is that several genes are involved in the cardiovascular control mechanisms and the genetics are complex. In addition, environmental factors that act over extremely long periods of time (such as diets, physical activity, stress) confound the genotype/phenotype relation individually, within a family, and regionally. So although monogenetic, dominant traits and diseases such as some lipid disorders can be studied with relative ease, polygenetic diseases like human primary hypertension remain puzzles for the future, making well-defined experimental models for research mandatory (for review, see References 1-3). In this review we will focus on three different types of experimental hypertension models, each model representing a specific stage of experimental hypertension research.We will discuss the spontaneously hypertensive rat (SHR), first described by Okamoto et al, 4 -5 which was obtained by selective breeding. This rat strain represents, in principle, an experiment of nature. Rats were selected from a normal colony for a specific phenotype, namely, high blood pressure. The hypertension of SHRs clearly is hereditary and genetically determined. These rats, therefore, provide an excellent model for the study of naturally occurring candidate hypertension genes that have accumulated in them. In fact, as will be discussed below, strain- specific structural differences in the renin gene have been found in SHRs.6 A further refinement in the generation of experimental animal models was the introduction by classic breeding of a mutated vasopressin gene into the genetic background of the SHR. Nature provided us with a mutation of interest for hypertension research: the Brattleboro rats, which exhibit a spontaneous point mutation of the vasopressin gene resulting in a shift of the reading frame and production of a nonfunctional, ineffective protein precursor. These animals produce no vasopressin (AVP) and have a hereditary hypothalamic diabetes insipidus (DI). Introduction of this defective gene into SHRs proved conclusively and definitely that AVP is not necessary for the elevation and maintenance of hypertension. The drawback of this approach is the necessity to wait for spontaneous and natural gene mutations before they can be introduced into new rat strains.With the availability of molecular biological approaches, it now is possible to design a more rational animal model. Gene technology makes it possible to introduce new, additional genes in normotensive and hypertensive animals. It also is possible, in the mouse, to delete or mutate specific genes, and similar technology is being developed for use in the rat. This marks the important t...

Beta-adrenergic neuroeffector mechanisms in cardiac hypertrophy of renin transgenic rats.

“…Recently, transgenic animals became available that overexpress mouse renin at particularly high concentrations in tissues, 14 including the myocardium (M. Paul, unpublished data, 1994). These animals develop cardiac hypertrophy and fulminant hypertension.…”

Reduced sodium-proton exchange activity in lymphocytes from transgenic rats.

“…TGR rats show a low plasma renin activity, an increased adrenal renin activity, and a decreased renal renin activity, but the pathophysiological basis for hypertension in these animals is unclear. 14 As to the alterations in Na + -H + exchange, no direct link to the insertion of the mouse renin gene in these animals is apparent. The findings therefore suggest that in TGR rats other alterations than those caused by the mouse renin gene may exist, whether they are independent of the presumed genetic alteration or somehow indirectly related.…”

Alterations in Sympathetic Ganglionic Transmission in Response to Angiotensin II in (mRen2)27 Transgenic Rats

“…The (mRen2)27 transgenic rat is characterized by overexpression of mouse Ren2 d gene in brain and adrenal gland, with a reduction of renin in the kidney. 22 A dependence of the hypertension on a centrally-mediated increase in SNA is reported. [23][24][25] Brain ventricular administration of an Ang II antibody lowers arterial pressure, as does anesthesia.…”