Inbred salt-sensitive (SS) rats developed by John Rapp and distributed by Harlan (SS/JrHsd) were shown to model ovariectomy-induced hypertension because on a low-sodium (LS) diet, ovariectomized SS (SS-OVX) animals became hypertensive in contrast to their sham-operated (SS-SHAM) normotensive littermates. After Harlan merged with Envigo in 2015, inconsistencies in the LS normotensive phenotype were reported. To further investigate these inconsistencies, we studied the effects of ovariectomy on SS and salt-resistant (SR) rats purchased from Envigo (SS/JrHsd/Env) between 2015 and 2017. The mean arterial pressure (MAP) in SS rats on a LS diet exceeded 160 mmHg at 7 mo old. Ovariectomy at 3 mo had no detectable effect on MAP from 4 to 7 mo, nor did ovariectomy at 1.5 mo significantly affect MAP at 10 mo in either strain; only strain differences in MAP were observed [MAP: SR-SHAM ( n = 7 rats), 102 ± 3 mmHg; SR-OVX ( n = 6 rats), 114 ± 1 mmHg; SS-SHAM ( n = 7 rats), 177 ± 6 mmHg; SS-OVX ( n = 5 rats), 190 ± 12 mmHg; where P < 0.0001 vs. SR, same ovarian-status for SS-SHAM and SS-OVX, respectively]. Whole genome sequencing revealed more genomic variants of SS/JrHsd/Env, including single nucleotide and insertion deletion polymorphisms and higher heterozygous/homozygous ratios compared with the reference genome, than for SS/JrHsd/Mcwi and SS/Jr rats maintained in Milwaukee, WI and Toledo, OH, respectively, and which still exhibit normal blood pressure on a LS diet. These findings demonstrate that the female SS/JrHsd/Env rat has genetically diverged from the original phenotype, which was normotensive on a LS diet when the ovaries were intact but rapidly developed hypertension when the ovaries were removed. Nonetheless, the SS/JrHsd/Env rat could be a valuable model that complements other animal models of spontaneous hypertension used to investigate mechanisms of essential hypertension.
Keywords: genetic drift; ovariectomy; spontaneously hypertensive rat.