E. E. Daniel

Electrolytes and Arterial Muscle Contractility

Arterial contractility in response to various drugs was studied in media designed to alter ionic gradients of sodium and potassium across the cell membrane. Tissues were analyzed to determine the effects of these procedures on tissue electrolytes and to demonstrate any correlation between tissue electrolytes and response. It was found that the contractile responses progressively decreased in sodium-free media, disappearing in 2 to 2½ hours. A decrease in external potassium, initially caused a potentiation of response. Thereafter, a decreased response was manifested, yet contractility remained even after 7 to 8 hours in potassium free medium. Increased external potassium caused an increase in response. There was no correlation between the content of sodium and potassium and response in potassium-free solutions, but in sodium-free solutions a positive correlation between contractility and potassium content existed. Chloride appeared to exist in 2 fractions, a diffusible fraction, and a more tightly bound fraction. Calculation of the ECFV based on the bound chloride yielded values which otherwise would have been absurd. Sodium appeared to be distributed in 3 fractions; diffusible and extracellular, not diffusible over the duration of our experiments and slowly diffusible and presumably intracellular, the latter fraction being possibly capable of cation exchange. Evidence obtained does not suggest that the sodium gradient, per se, is responsible for contractility. The concentration of intracellular potassium does not influence contractility directly. However, the potassium gradient may in part determine vascular muscle contractility.

Effect of the placenta on the electrical activity of the cat uterus in vivo and in vitro

Abstract 1. The electrical activity of the pregnant cat uterus consists of repetitive action potentials which appear to be conducted and to initiate a prolonged contraction. 2. In vitro, myometrium which had been over the placenta was less excitable by stretch. Action potentials fail to occur in these areas or spread to placental myometrium only secondarily. 3. In vivo, myometrium over the placenta showed little or no spontaneous activity before term and likewise usually failed to respond to intramuscular injections of Pitocin (0.025 to 0.25 units) which activated myometrium in other areas. At term, the distinction between the electrical excitability of placental and nonplacental myometrium disappeared. 4. The ionic composition and the ionic exchanges in placental myometrium differed from the composition and exchanges in other myometrium in a manner which suggested that placental myometrium was under the influence of progesterone. 5. These results were considered to support the hypothesis that the local inhibitory action of placental progesterone may be important in preventing abortion before term and that the withdrawal of that action may play a role in initiating labor.

Vascular Muscle Reactivity

Arterial contractility was investigated, using spiral and ring sections of dog, cat, rabbit, rat, and human vessels. Epinephrine produced contractions of all arterial tissue tested. Histamine invariably produced contractions. The phenomenon of variable sensitivity of arterial tissue to histamine was again demonstrated. Acetylcholine caused contractions of rabbit, cat, and rat aortas, but no contraction of the dog aorta, or dog and human femoral arteries was observed. Pitressin produced contraction of the rat aorta, and dog and human femoral arteries, but not of rabbit, dog or cat aortas. Using dog vessels, a difference in activity was observed between the aorta and the femoral artery. Greater reactivity in terms of maximum rate of tension increase and tension developed was seen in the smaller systemic arteries. A pharmacologic difference with respect to the action of pitressin was discovered between the aorta and the smaller arteries. Thus, general evidence is presented suggesting that data obtained in 1 species of animal on 1 type of tissue cannot be transferred without specific proof of its validity to data obtained in other species, or even in closely related tissues of the same species. An apparent antagonistic effect of pitressin on the pressor action of epinephrine was detected.

Electrolyte in human myometrium

Abstract 1. 1. Analyses were carried out of the water, chloride, sodium, and potassium concentration of biopsy specimens of human myometrium. Comparisons were made between the values found in various stages of the menstrual cycle, in menopause, in pregnancy, and in other various pathological states. Comparisons were also made of the values found in the various portions of the corpus (the upper, mid, and lower uterine segments). 2. 2. In menopause, the myometrium was found to contain a low water concentration relative to other states and to have higher concentrations of those electrolytes (Na and Cl) which are present in high concentrations in the extracellular fluid. Correspondingly, it had lower concentrations of potassium, a component concentrated in cellular fluid. 3. 3. In the proliferative and secretory stages of the menstrual cycle there was a higher concentration of water and of potassium in the myometrium than in menopause. The concentrations of sodium and of chloride tended to be lower; the water concentrations of the myometrium was highest in the mid and late proliferative phases. Potassium concentration was highest in the late secretory phase. Concentrations of sodium and chloride did not vary significantly during the cycle, but sodium concentration tended to be lower in the mid and late proliferative than in the secretory states. 4. 4. In pregnancy, at term but before the onset of labor, the potassium and water concentrations of the myometrium are as high as or higher than in any stage of the menstrual cycle. The water concentration of the lower uterine segment is remarkably elevated compared to the nonpregnant state, and this change is accompanied by an increase in concentrations of sodium and of chloride. 5. 5. The lower uterine segment was found to contain less water and sometimes less potassium than the upper and midsegments in all conditions studied except in pregnancy at term. 6. 6. Various pathological myometria have been analyzed and the results discussed as illustrative of a possible insight to be gained by such analyses into mechanisms operating in uterine pathology. 7. 7. Finally, the implications of these results with regard to current hypotheses as to the mechanism of action of ovarian hormones and as to the differences in mechanical activity of various uterine segments have been discussed.