Life Scieacae Vol . 20, pp . Printed in the U.S .A.
1239-1248, 1977 .
Pergamon Praee
RESISTANCE OF FISCHBR 344 RATS Ta DEOXYCORTIC03TERONB HYPERTENSION
Charles B . Hall and Octavia Hail Department of Physiology and Biophysics University of Texas Medical Branch Galveston, Texas
77550
(Received in final form February 28, 1977) Implantation of one 40 mg pellet of DOCA causes hypertsnaioa is the majority of young female Sprague-Dawley rata within three weeks without removal of a kidney or adding salt to the diet . Similar identically-treated Rather 344 rats remain normotenaive . If one kidney is roved and is saline is given to drink, the hormone dosage causes hypertension in rats of both strains, although even here Fischer 344 rats develop the disorder more slowly and less severely . It is concluded that for rat strains resistant to mineralocorticoid hypertension, sensitization is necessazy for its induction, whereas for susceptible strains it is not. Fischer 344 rats appear to have higher levels of resting serum resin activity than Sprague-Dawley rats, but the relationship that this bears to hypertension susceptibility is unknown . The prolonged ingestion of excessive NaCl causes hypertension in many strains of rat (1-4) . The involvement of a genetic factor in susceptibility is demonstrated by the fact that bY selective breeding of suitable progenitors, sub-strains can be developed which are either susceptible or resistant to the disorder (5) . Certain rat strains such as inng-Evens (6,7) and Fischer 344 (6, 8) restrict intake of 1~ saline when salt excess is provided thus, and remain normoteneive . If sucrose ie added to saline solution, intake is augmented by the ensuing polydipeia . Under such circumstances Lonq-Evens rats become hypertenaive (9), whereas Fischer 344 rate do not (10) . The latter display resistance to salt hypertension comparable to rats of Dahl's "resistant" substrain which withstand an eztremely high salt intake for extended periods without appreciable blood pressure elevation (11) . Salt-resistant Iong-Beans rata also oppose hypertension usually induced by deoxycorticostemne acetate (DOCA) and salt (7), although they are susceptible to adrenal-regeneration hypertension (12) . Fischer 344 rats have been shown also to be susceptible to adrenal-regeneration hypertension (13), and it was a purpose of the present study to test their auaceptibility to DOCA hypertension. Materiale and Methods Five~eek old female rats of the Fischer 344 and SPD strains were obtained from the AILS 3praque-Dawley Company . in each of the following experiments, groups of each strain were utilized . 1239
1240
Fischar 344 Rate and DOCA Hypertension
Vol . 20, No . 7, 1977
Sz~eriment 1 Seventeen female Fischer 344 and sixteen 5PD rats were each divided into two groups, as indicated in Table 1 . Nine of the former and eight of the latter each had one 40 mq pellet of DOCA* implanted subcutaneously between the scapulae . Sach rat in these groups also received 5 mq of DOCA in sesame oil aubcutaneously on the 50th and 57th days, since the blood pressure response had plateaued . Sight rata of each strain served ae controls . Rats were given tap water and Purina Laboratory Chow _ad libitum , and individually caged in temperature-controlled quarters . Systolic pressures were measured before beginning treatment, and weekly thereafter in conscious animals by the tail-cuff method using a programmed electroaphygmomanometer and a Physiograph 4 (Marco Biosystems, Houston, Texas) . In each case between 3 and 8 individual consecutive pressures were averaged to obtain the mean . values above 150 mm Hg were regarded as hypertensive . The animals were killed on the 64th day by guillotine decapitation and trunk blood was collected within 5 sec into chilled plastic containers . Following coagulation, cells and serum were separated at -lOoC in a refrigerated centrifuge . A sample of serum was removed for measurement of Na+ and 1cF by flame photometry (Beal®an 1ä1m Flame) . The remainder was transferred to chilled plastic vials and frozen at -20oC until serum resin activity (SRA) was measured (14) . Various organs were removed from the trunks and placed in neutral 108 formalin for subsequent weight . When fixed they were removed, trimmed, blotted, and weighed on an analytical balance . S:ami.nation of the organs at necropsy did not reveal visible lesions in the hearts or kidneys of any rat . Sx~eriment 2 Sighteen female rats of the Rather 344 strain and an equal number of similar SPD rats were used . Three equal groups ware constituted from each strain, groups 1-3 being Fischer 344 and getups 4-6 SPD rats . All were mono nephreotomized (right) under ether anesthesia. Groups 1 and 4 were given tap water to drink and groups 2, 3, 5 and 6 received la saline solution . One 40 m9 pellet of DOCA was implanted subcutaneously into rata of groups 3 and 6 . The animals were fed sad housed ae in the preaedinq experiment . Systolic blood pressures were obtained at intervals using the methods and adopting the criteria described in the first experiment . Fluid consumption was tabulated on three consecutive days of each week prior to the day of blood pressure measurement . The mean of these figures was taken as representative for the week . The rats were killed by over-etherization on the 26th day . Various organs were removed and processed as in the foregoing experiment . Student's two-tailed "t" feet was used for statistical analysis . Results In the first experiment there were no significant differences between the mean systolic blood pressures of the various groups prior to treatment . As the * Generously supplied by the Ciba-Geigy Corporation, Ardeley, New York .
Vol . 20,
lao .
7, 1977
Fischer 344 Bats and DOCH Hypertension
1241
rats grave, blood presence of ccntml rats, and of DOG-treated Fischer 344 rata, increased from about 90-95 est Hq to about 120-125 over a three-wek period . From then on it retained relatively stable, fluctuating very little . DOGtreated SPD rata, by contrast, had beccae mildly but definitely hypertenaiva by three reeks of treatment (Fig. 1) . Five ani~al.e, or 63t of the group, reacted in that +~"^r .r whereas the other three resained normotansive . 11n additional siz reeks of treatment, and 5 mg dosages of DOG at the begiaainq of each of the last tro reeks, had no appreciable further affect on the incidence or severity of hypertension in SPD rats, nor on the aorsal blood pressure of Fischer 344 w^i,~+" iw . One DOG-treated SPD rat which had bean aormoteasive at the 3rd reek shaved mild hypertension on the 5th and 7th reek, but was norsotensive at the Sth and 9th reek and so classified . statistical analysis revealed that the blood pressure of DOC11-treated Fischer 344 rats differed significantly from controls (P < 0 .05) at only the second and third reeks Then adult blood pressures rare being developed . The couparable SPD group, by cozttraat,ras significantly higher at each period (2-9) during hormone treatment (P < 0 .003) . FISCHER
344
SPRAßUE-DAWLEY
"-~ DOCA "----" UNTREATED
N
1
3
S
7
9 1 WEEK
S
Fiq . 1 Systolic arterial pressure in hormone-treated and control rata . First arrow indicates time of pellet implantation, second sad third arrays the time of subcutaaeoua ho +~+nw injections . The Na+ values of saran collected at autopsy cars about 20 ~4/L lower than could have been effected frost heart blood, and the 1Cf concentrations about double heart blood values . This matter has been discussed elseHhere (15), and doubtless reflects the contamination of blood by intracellular fluids, law in sodium and high is potassium, from cellular disruption incident to decapitation . Despite this, DOG treats~eat caused a alight, though statistically insignificant elevation of semen äa+ and a oonaiderable and aigaificant depression of serum ~1C+ (Table 1) . The testing setae ream activity of Fisohsr 344 rats was significantly elevated, about twfold, above that of SPD rats . DOC71 treatment depressed the level in both attains to the same lov values, although the actual drop, and the magnitude Of the diflereace between treated and control w^iAwiw , was much greater in Fischer 344 rata because of their higher initial values
1242
Fischer 344 Rate and DOCA Hyperteaeion
Vol . 20, No . 7, 1977
(Table 1) . SRA vas undetectable in DOCA-treated rats . The depression, while obvious, could not be treated by parametric statistics . TABLE I Serum Electrolytes and Benin Activity in DOCH-treated and Control Rats Data Na+
Fischer 344 Controls DOCA
123 ± 0.8a 125 t 2 .0 m8q/L K+ 6 7.1 t O.lc 6 .5 t 0.2b Renin Activity nq/ml/hr 4.23 t 0.58c
1239-1248, 1977 .
Pergamon Praee
RESISTANCE OF FISCHBR 344 RATS Ta DEOXYCORTIC03TERONB HYPERTENSION
Charles B . Hall and Octavia Hail Department of Physiology and Biophysics University of Texas Medical Branch Galveston, Texas
77550
(Received in final form February 28, 1977) Implantation of one 40 mg pellet of DOCA causes hypertsnaioa is the majority of young female Sprague-Dawley rata within three weeks without removal of a kidney or adding salt to the diet . Similar identically-treated Rather 344 rats remain normotenaive . If one kidney is roved and is saline is given to drink, the hormone dosage causes hypertension in rats of both strains, although even here Fischer 344 rats develop the disorder more slowly and less severely . It is concluded that for rat strains resistant to mineralocorticoid hypertension, sensitization is necessazy for its induction, whereas for susceptible strains it is not. Fischer 344 rats appear to have higher levels of resting serum resin activity than Sprague-Dawley rats, but the relationship that this bears to hypertension susceptibility is unknown . The prolonged ingestion of excessive NaCl causes hypertension in many strains of rat (1-4) . The involvement of a genetic factor in susceptibility is demonstrated by the fact that bY selective breeding of suitable progenitors, sub-strains can be developed which are either susceptible or resistant to the disorder (5) . Certain rat strains such as inng-Evens (6,7) and Fischer 344 (6, 8) restrict intake of 1~ saline when salt excess is provided thus, and remain normoteneive . If sucrose ie added to saline solution, intake is augmented by the ensuing polydipeia . Under such circumstances Lonq-Evens rats become hypertenaive (9), whereas Fischer 344 rate do not (10) . The latter display resistance to salt hypertension comparable to rats of Dahl's "resistant" substrain which withstand an eztremely high salt intake for extended periods without appreciable blood pressure elevation (11) . Salt-resistant Iong-Beans rata also oppose hypertension usually induced by deoxycorticostemne acetate (DOCA) and salt (7), although they are susceptible to adrenal-regeneration hypertension (12) . Fischer 344 rats have been shown also to be susceptible to adrenal-regeneration hypertension (13), and it was a purpose of the present study to test their auaceptibility to DOCA hypertension. Materiale and Methods Five~eek old female rats of the Fischer 344 and SPD strains were obtained from the AILS 3praque-Dawley Company . in each of the following experiments, groups of each strain were utilized . 1239
1240
Fischar 344 Rate and DOCA Hypertension
Vol . 20, No . 7, 1977
Sz~eriment 1 Seventeen female Fischer 344 and sixteen 5PD rats were each divided into two groups, as indicated in Table 1 . Nine of the former and eight of the latter each had one 40 mq pellet of DOCA* implanted subcutaneously between the scapulae . Sach rat in these groups also received 5 mq of DOCA in sesame oil aubcutaneously on the 50th and 57th days, since the blood pressure response had plateaued . Sight rata of each strain served ae controls . Rats were given tap water and Purina Laboratory Chow _ad libitum , and individually caged in temperature-controlled quarters . Systolic pressures were measured before beginning treatment, and weekly thereafter in conscious animals by the tail-cuff method using a programmed electroaphygmomanometer and a Physiograph 4 (Marco Biosystems, Houston, Texas) . In each case between 3 and 8 individual consecutive pressures were averaged to obtain the mean . values above 150 mm Hg were regarded as hypertensive . The animals were killed on the 64th day by guillotine decapitation and trunk blood was collected within 5 sec into chilled plastic containers . Following coagulation, cells and serum were separated at -lOoC in a refrigerated centrifuge . A sample of serum was removed for measurement of Na+ and 1cF by flame photometry (Beal®an 1ä1m Flame) . The remainder was transferred to chilled plastic vials and frozen at -20oC until serum resin activity (SRA) was measured (14) . Various organs were removed from the trunks and placed in neutral 108 formalin for subsequent weight . When fixed they were removed, trimmed, blotted, and weighed on an analytical balance . S:ami.nation of the organs at necropsy did not reveal visible lesions in the hearts or kidneys of any rat . Sx~eriment 2 Sighteen female rats of the Rather 344 strain and an equal number of similar SPD rats were used . Three equal groups ware constituted from each strain, groups 1-3 being Fischer 344 and getups 4-6 SPD rats . All were mono nephreotomized (right) under ether anesthesia. Groups 1 and 4 were given tap water to drink and groups 2, 3, 5 and 6 received la saline solution . One 40 m9 pellet of DOCA was implanted subcutaneously into rata of groups 3 and 6 . The animals were fed sad housed ae in the preaedinq experiment . Systolic blood pressures were obtained at intervals using the methods and adopting the criteria described in the first experiment . Fluid consumption was tabulated on three consecutive days of each week prior to the day of blood pressure measurement . The mean of these figures was taken as representative for the week . The rats were killed by over-etherization on the 26th day . Various organs were removed and processed as in the foregoing experiment . Student's two-tailed "t" feet was used for statistical analysis . Results In the first experiment there were no significant differences between the mean systolic blood pressures of the various groups prior to treatment . As the * Generously supplied by the Ciba-Geigy Corporation, Ardeley, New York .
Vol . 20,
lao .
7, 1977
Fischer 344 Bats and DOCH Hypertension
1241
rats grave, blood presence of ccntml rats, and of DOG-treated Fischer 344 rata, increased from about 90-95 est Hq to about 120-125 over a three-wek period . From then on it retained relatively stable, fluctuating very little . DOGtreated SPD rata, by contrast, had beccae mildly but definitely hypertenaiva by three reeks of treatment (Fig. 1) . Five ani~al.e, or 63t of the group, reacted in that +~"^r .r whereas the other three resained normotansive . 11n additional siz reeks of treatment, and 5 mg dosages of DOG at the begiaainq of each of the last tro reeks, had no appreciable further affect on the incidence or severity of hypertension in SPD rats, nor on the aorsal blood pressure of Fischer 344 w^i,~+" iw . One DOG-treated SPD rat which had bean aormoteasive at the 3rd reek shaved mild hypertension on the 5th and 7th reek, but was norsotensive at the Sth and 9th reek and so classified . statistical analysis revealed that the blood pressure of DOC11-treated Fischer 344 rats differed significantly from controls (P < 0 .05) at only the second and third reeks Then adult blood pressures rare being developed . The couparable SPD group, by cozttraat,ras significantly higher at each period (2-9) during hormone treatment (P < 0 .003) . FISCHER
344
SPRAßUE-DAWLEY
"-~ DOCA "----" UNTREATED
N
1
3
S
7
9 1 WEEK
S
Fiq . 1 Systolic arterial pressure in hormone-treated and control rata . First arrow indicates time of pellet implantation, second sad third arrays the time of subcutaaeoua ho +~+nw injections . The Na+ values of saran collected at autopsy cars about 20 ~4/L lower than could have been effected frost heart blood, and the 1Cf concentrations about double heart blood values . This matter has been discussed elseHhere (15), and doubtless reflects the contamination of blood by intracellular fluids, law in sodium and high is potassium, from cellular disruption incident to decapitation . Despite this, DOG treats~eat caused a alight, though statistically insignificant elevation of semen äa+ and a oonaiderable and aigaificant depression of serum ~1C+ (Table 1) . The testing setae ream activity of Fisohsr 344 rats was significantly elevated, about twfold, above that of SPD rats . DOC71 treatment depressed the level in both attains to the same lov values, although the actual drop, and the magnitude Of the diflereace between treated and control w^iAwiw , was much greater in Fischer 344 rata because of their higher initial values
1242
Fischer 344 Rate and DOCA Hyperteaeion
Vol . 20, No . 7, 1977
(Table 1) . SRA vas undetectable in DOCA-treated rats . The depression, while obvious, could not be treated by parametric statistics . TABLE I Serum Electrolytes and Benin Activity in DOCH-treated and Control Rats Data Na+
Fischer 344 Controls DOCA
123 ± 0.8a 125 t 2 .0 m8q/L K+ 6 7.1 t O.lc 6 .5 t 0.2b Renin Activity nq/ml/hr 4.23 t 0.58c
