Vascular and cardiac effects of stress in albino rats of different sex and age groups.

Stress exposure induced similar cardiac effects in male and female infantile rats, but vascular reactions to stress in males were more pronounced than in females. In mature male rats (but not in females), both cardiac and vascular responses to stress decreased in comparison with infantile animals. In adult rats, cardiac effects of stress were more pronounced than the vascular response; females demonstrated greater cardiac response and less significant vascular reactions than males. Aging was accompanied by a decrease in the cardiac response and increase in the vascular reaction to stress. These changes were more significant in females than in males. In contrast to infantile and adult animals, old females demonstrated greater vascular response to stress than male rats. The observed sex-dependent changes in the ontogeny of vascular and cardiac response to stress are discussed in light of sex- and age-related peculiarities of hypertension development.

Mechanisms for vascular effects of androgens in normotensive and hypertensive rats.

Castration had no effect on baseline BP and vascular sensitivity to acetylcholine and deficiency of nitric oxide and prostacyclin in normotensive specimens. Castration of hypertensive specimens decreased BP and potentiated the hypotensive effects of acetylcholine, but did not modulate vascular sensitivity to the blockade of nitric oxide and prostacyclin synthesis. The removal of the testicles abolished the pressor influence of glybenclamide in hypertensive and, particularly, in normotensive males. These data indicate that the non-endothelial vascular effects of androgens (i.e., stimulation of K(ATP) channels) predominate under normal conditions. The activating effects of androgens on K(ATP) channels decrease during hypertension, which is accompanied by inhibition of endothelium-dependent vasorelaxation. The production of nitric oxide and prostacyclin remains unchanged under these conditions. Our results suggest that endothelium-derived hyperpolarizing factor is involved in these processes.

Effect of age and sex on blood pressure, development of renal hypertension, and concentration of nitric oxide in the blood of albino rats.

The mean blood pressure did not depend on the sex of animals and was characterized by the same ontogenetic changes in males and females. The mean blood pressure in infantile and, particularly, in old rats was higher than in adult animals. The increase in blood pressure in old rats was accompanied by a decrease in NO production. Infantile rats were least resistant to the development of renal hypertension. The degree of hypertension in infantile and adult females was lower than in males. However, the concentration of NO in these females was higher than in male rats. Aging was accompanied by inversion of sex differences in the resistance to renal hypertension. The severity of hypertension in old females was greater than in males. It was accompanied by a significant age-related decrease in NO concentration in female animals. Our results indicate that NO plays an important role in sex differences in the resistance of infantile, adult, and old rats to hypertension, while the decrease in NO concentration during aging leads to blood pressure elevation in females and males.

Sex-specific peculiarities of cholinergic regulation of the cardiovascular system in normal and hypertensive rats.

Cardiovascular sensitivity to atropine and acetylcholine is reduced in renal hypertension. Hypertension in females is more benign and the hypotensive effects of acetylcholine in them are less attenuated than in males. Cardiovascular sensitivity to cholinergic effects in females is higher in health and hypertension, which improves their resistance to cardiovascular pathology.

Sex-related differences in cardiovascular stress reactivity in healthy and hypertensive rats.

In healthy females the chronotropic effects of stress are more pronounced, while the hypertensive effects are weakened compared to males. Hemodynamic parameters in females returned to normal more rapidly than in males. Renovascular hypertension in males is more pronounced than in females and is associated with increased cardiovascular stress reactivity (in females it is associated with decreased cardiovascular stress reactivity), which increase the risk of cardiovascular complications in males.

Role of sex hormones in cardiovascular resistance to atropine in rats at rest and during stress.

Castration of males and females reduces the sensitivity of cardiac chronotropic function to atropine and potentiates the vascular component in the reaction to atropine in females (during stress) and males (at rest and during stress). Our results show that estrogens and androgens increase the sensitivity of the cardiovascular system to cholinergic influences at rest and during stress.

Sex-related differences in nitric oxide content in healthy and hypertensive rats at rest and under stress conditions.

Immobilization was followed by an increase in blood NO concentration in male and female rats. After renovascular hypertension modeling blood pressure was higher and the decrease in nitric oxide concentration was more pronounced in males than in females. The levels of nitric oxide in healthy and hypertensive females at rest and during stress were higher than in males. These specific features probably contribute to higher resistance of the cardiovascular system in females to pathological changes.

[Sex differences in the cholinergic status of white rats]. / Polovye razlichiia kholinergicheskogo statusa u belykh krys.

Female rats injected with organophosphate inhibitor of acetylcholinesterase chlorophose at doses of 10 mg/kg and 360 mg/kg showed less considerable decrease in blood acetylcholinesterase activity than did male animals. Females compared with males also demonstrated less expressed clinical symptoms of poisoning (salivation, convulsion) after injection of chlorophose at dose of 360 mg/kg. The value of LD50 in female rats was 860 mg/kg, whereas the comparable value in male animals was 700 mg/kg. Following the injection of atropine at doses of 0.1, 0.3, 0.6 mg/100 g female rats showed 2-3 fold increases in basal adrenal and plasma corticosterone levels, but significant decreases in stress-induced corticosterone levels. As for males, the basal and stress-induced values of corticosterone were not significantly affected by atropine administration. These results suggest that functional reserves of cholinergic system and responsiveness of the hypothalamic-pituitary-adrenal axis to cholinergic influence are greater in females than in males. It is concluded that cholinergic status is significantly higher in female rats than in male ones.

[Sex differences in adrenocortical sensitivity and resistance to cerebrovascular damage in rats under strong stress]. / Polovye razlichiia adrenokortikal'noi chuvstvitel'nosti i ustoichivosti k tserebrovaskuliarnym povrezhdeniiam u krys pri sil'nom stresse.

Dynamics of changes in adrenal and plasma corticosterone and the development of cerebrovascular lesions were studied in both male and female rats, exposed to strong stress (combined immobilization and intermittent found sound for 2 hours). Plasma corticosterone levels in stressed females were 460% and 660% of the control values when measured on stress minute 10 and 120. The corresponding values in male rats were 220% and 360%. The stress-induced dilatation of brain vessels and the increases in vascular permeability were less pronounced in females than in males, when studied 0.1 and 24 hours after termination of stress. The number of brain perivascular haemorrhages was markedly reduced in females compared with males. It is supposed that higher resistance to stress-induced cerebrovascular lesions in females may be attributed to higher functional reserves of steroidogenesis.

[Sex differences in response to adrenaline in white rats]. / Polovye razlichiia v chuvstvitel'nosti belykh krys k adrenalinu.

Dynamics of changes of and plasma corticosterone was studied in both male and female rats after intraperitoneal injections of adrenaline at a dose of 20 micrograms per 100 g body weight. The control rats were injected with saline. Animals were decapitated 10, 30, 60, 120, 180 and 240 min after the injections. The specific effect of adrenaline was revealed in the first 10 min of adrenaline injection. This effect was significantly increased to 30-60 min after termination of saline--induced activation of the pituitary-adrenal axis. Both saline and adrenaline caused more significant increases in corticosterone levels in female rats than in male ones. There was a significant delay in the return of corticosterone to resting levels in males compared to that in females. It is supposed that the almost two-fold difference in peak plasma corticosterone concentrations observed after stressors may be associated with increased responsiveness of the female hypothalamus with respect to adrenaline secretion.

[Sex differences in response to stress in conscious and anesthesized rats during surgical stress]. / Polovye razlichiia v stress-reaktivnosti u bodrstvuiushchikh i anestezirovannykh krys pri khirurgicheskom stresse.

Adrenal and plasma corticosterone levels under conditions of preoperative stress (removal from animal to experimental rooms, removal from a home cage, handling, weighing and injecting with saline) were more than 2-fold higher in female rats than in male ones. Females, compared with males, showed more pronounced decrease in corticosterone responses to preoperative stress and laparotomy under nembutal anesthesia, which blocked stress-induced emotional activation. One hour after recovery from anesthesia laparotomized females but not males, demonstrated a significant (5-fold) increase in plasma corticosterone level. The absolute values of plasma corticosterone in laparotomized females, compared with males, were 2-fold lower under anesthesia but 2-fold higher after recovery from anesthesia. It is supposed that in females, compared with males, stress-induced emotional tension plays more considerable role in endocrine stress responses. This provides higher adrenocortical sensitivity to stress in conscious female rats than in male animals.

[Sex differences in reserve capacity of the pituitary-adrenal system in rats]. / Polovye razlichiia rezervnykh vozmozhnostei gipofizarno-adrenokortikal'noi sistemy u krys.

Female rats exposed to complex emotional stress for 1 hour (restriction in the penal, vibration, loud dissonance music, interrupt light) simultaneously showed more considerable increases in plasma and adrenal corticosterone values than did male animals. Female rat corticosterone levels returned to basal values within 20-120 minutes of stressor-off. As for males the processes of restoration were delayed and accompanied by a 6-fold decrease in the plasma corticosterone levels compared with basal values. The response to additional acute stress (immobilization for 10 minutes) in various times after termination of complex emotional stress (0, 40, 120, 180, 240 minutes) was facilitated in females and remained unchanged in males. Plasma corticosterone levels under stressful conditions were 2-4-fold higher in females than in males. It is concluded that reserve capacity of adaptation system is significantly higher in female rats than in male ones.

[Sex differences in the dynamic response reactions to emotional stress exposures in white rats]. / Polovye razlichiia dinamiki otvetnykh reaktsii na émotsional'nye stressornye vozdeistviia u belykh krys.

The changes of adrenal and plasma corticosterone and adrenal catecholamines were studied in male and female rats during and after short-term (10 min) emotional stress (the sight and squeals of immobilised partners) and emotional-pain stress (immobilisation). Obvious sexual differences in the stress reactions were revealed: females developed the greatest increase in corticosterone levels which returned to initial values within 40-60 min after cessation of the stress. Concentrations of adrenaline decreased in the first 5 min of stress and became normal by the 10th min. Males developed the greatest increase in the corticosterone levels not during stress but 20-40 min after termination of the stressful stimulus. The adrenaline level increased by the 10th min of stress and became normal within 20 min of poststress period. The advantage of "female's" strategy in stress reactions is discussed.

[Sex differences in the age-related dynamics of the reactivity to physiological stressors in white rats]. / Polovye razlichiia vozrastnoi dinamiki reaktivnosti k fiziologicheskim stressoram u belykh krys.

After removal of habitual partners, white female rats revealed a considerable increase in the corticosterone synthesis and secretion. An increase in the hormone secretion but not in its synthesis occurred in young male rats. In ageing male rats, emotional stress induced an increase in the corticosterone synthesis but the hormone did not enter their blood. High responsiveness of the adaptation systems was revealed in female rats through modification of their basal and stress-induced levels of corticosterone during a 72-hour exposure to light and darkness.

[Analysis of factors determining sex differences in stress reactions of white rats]. / K analizu faktorov, determiniruiushchikh polovye razlichiia v stressovykh reaktsiiakh u belykh krys.

Female rats demonstrate more considerable increasing of corticosterone synthesis and secretion in comparison with male ones under the conditions of emotional and emotion-pain stress. These differences are not disappeared after castration. The sexual differences in stress reactions of infants are accompanied by lower sensitivity of their adaptation system in relation to stressors. The adult neonatal androgenized females show the same reactivity as normal females under the condition of emotion-pain stress. It is concluded that the sexual differences in stress reactions are genetically determined.

[Sexual dimorphism in reactions to stress during regular and altered photoperiods]. / Polovoi dimorfizm v stressornoi reaktsii pri obychnom i izmenennom fotoperiode.

Sexual dimorphism of rats in response to physiological stress influences was discovered. The emotional stress in female animals caused a sharp intensification of synthesis and corticosterone secretion, while in males there was an increase only in hormone synthesis and not its secretion. Females are more sensitive even to short-term changes in photoperiod. Stress reaction in females under conditions of three-day light depressed sharply and increased under conditions of three-day darkness. Stress reaction in males did not change under these conditions. The reactivity of adaptation system in females shortens the period of adaptation to the altered illumination regimen, which is manifested in the restoration of typical stress reactions. In males, refractoriness to weak stress influences lengthens the period of adaptation, which is manifested in the suppression of typical stress reaction observed in males.

[Reaction of the ovary of the young rat to transplantation into the spleen of adult castrated diabetic animals]. / Reaktsiia iachnika infantil'noi krysy na transplantatsiiu v selezenku vzroslykh kastrirovannykh diabeticheskikh zhivotnykh.

The ovary of an infantile rat was grafted into the spleen of adult castrated females. After 7-9 days half of the animals were injected with alloxan subcutaneously. The rats were decapitated 33 days after ovary grafting. In all diabetic rats and 62% of the control animals, the vaginal smears showed persistent diestrus. The height of the uterine epithelium was fairly low. Persistent estrus was detected in 38% of the control animals. In the diabetic group, the degree of ovarian hypertrophy was significantly lower than in the control group, although no differences were discovered in pituitary gonadotropin content in both the groups. It is suggested that the pituitary of diabetic animals slightly responds to estrogenic deficiency. This was manifested in a lesser degree of ovarian hypertrophy and in the absence in the ovaries of the majority of diabetic rats of the phenomena such as the proliferation of the connective tissue and the appearance of granulocellular tissue accumulations.

[Compensatory ovarian hypertrophy during alloxan diabetes and adrenoreceptor blockade]. / Kompensatornaia gipertrofiia iaichnika v usloviiakh alloksanovogo diabeta i blokady adrenoretseptorov.

The sexual cycle ceases in rats with alloxan diabetes. Chronic administration of phentolamine promoted interruption of the sexual cycle while obsidan was conducive to its preservation in part of the animals. Most diabetic rats both given and not given adrenoblockers showed the complete absence of compensatory hypertrophy of the ovary (CHO). As shown by the analysis, the content of gonadotropins in the pituitary glands of diabetic rats was increased, with the response to chorionic gonadotropin being close to normal. It is suggested that the absence of CHO in most diabetic rats can be accounted for by the fact that after removal of one ovary the hypothalamohypophyseal system does not secrete gonadotropins in adequate amounts.