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Biomedical subjects

A Johns

Publications and source records attributed to A Johns.

126 records · Page 7Linked to original sources
PubMed1975

The effect of caesium on adrenergic transmission in rabbit vas deferens.

The effect of caesium on the responses of rabbit vas deferens to transmural stimulation was investigated. The tissue responded to transmural stimulation with a phasic spike contraction followed bya sustained contractile response. The sustained response was inhibited by phentolamine and guanethidine and thus apparently results from noradrenaline release from adrenergic nerves. Addition of 2-5mM Cs+ greatly potentiated this secondary response without altering the sensitivity of the tissue to added (minus)-noradrenaline. This potentiation was not due to Cs+ decreasing the neuronal uptake of noradrenaline, or by Cs+ altering prostaglandin synthesis. Addition of 2mM Cs+ significantly increased the amount of (plus or minus)-[3-H] metaraminol released from tissues in response to transmural stimulation (5 Hz). It is suggested that caesium potentiated responses of rabbit vas deferens to transmural stimulation by increasing the amount of transmitter released per nerve impulse, possibly as a result of prolongation of the action potential.

Action Potentials↗
PubMed1975

Effect of cocaine and other drugs on sensitivity of the estrogen-dominated isthmus of rabbit oviduct to noradrenaline.

The influence of the adrenergic innervation on the magnitude of responses of the isthmus of rabbit oviduct to (-)-noradrenaline was examined. Tissues were obtained from estrogen-dominated animals, and isometric contractions of longitudinal and circular muscle layers separately recorded. Longitudinal muscle was significantly more sensitive to (-)-noradrenaline. Cocaine potentiated responses of both corcular and longitudinal muscle to (-)-noradrenaline, circular muscle being more potentiated. Similar results were obtained with desipramine. Tissues obtained from 6-hydroxydopamine pretreated animals did not respond to tyramine, and longitudinal and circular muscles were equisensitive to (-)-noradrenaline. Cocaine did not potentiate responses to (-)-noradrenaline in such tissues. Responses to (-)-noradrenaline were not altered by propranolol, hydrocortisone, or oxytetracycline. It was concluded that responses resulted from a predominant effect on alpha-receptors. The magnitude of responses to (-)-noradrenaline was mainly influenced by neuronal uptake of amine. Indirect evidence was obtained for a greater degree of adrenergic innervation to the circular muscle layer of the isthmus, in keeping with histological studies.

Animals↗
PubMed1975

Effects of prostaglandin E2 and indomethacin on responses of the isthmus of rabbit oviduct to norepinephrine and transmural stimulation.

The effects of prostaglandin E2 and of indomethacin on the responses of the circular muscle of the isthmus of rabbit oviduct to (-)-norepinephrine and to transmural stimulation were determined. At 26 degrees C, 10 ng/ml prostaglandin E2 significantly reduced responses to transmural stimulation but had little effect on responses to (-)-norepinephrine. At 26 degrees C, 5.6 x 10(-5)M indomethacin slightly reduced responses to both transmural stimulation and to (-)-norepinephrine. At 37 degrees C, spontaneous desensitization to both stimulation and to (-)-norepinephrine occurred but transmural stimulation was more inhibited. Addition of 2.8 x 10(-6)M indomethacin prevented this desensitization. These results suggest that responses of the isthmus of rabbit oviduct to (-)-norepinephrine were not dependent on prostaglandin generation. Adrenergic transmission to the oviduct was, however, inhibited by prostaglandin E2. Evidence was also obtained for the spontaneous liberation at 37 degrees C of prostaglandins that inhibited the contractility of the oviduct.

Animals↗
PubMed1975

Characteristics of uptake of [3-H](plus or minus)-metaraminol by human fallopian tube.

The characteristics of accumulation of 5 X 10 minus8M [3-H] (plus or minus)-metaraminol were studied in isolated human fallopian tube. In both the ampulla and isthmus, the amine was concentrated against the concentration gradient; Accumulation was inhibited by noradrenaline, cocaine, and ouabain but not by oxytetracycline or normetanephrine. It was concluded that [3-H] (plus or minus)-metaraminol was accumulated in the adrenergic nerves present in the human fallopian tube.

Cocaine↗
PubMed1975

Pharmacological characteristics of the responses of rabbit oviduct to transmural stimulation.

The nature of the response of oestrogen dominant rabbit oviduct to transmural stimulation has been investigated. Both ampulla and isthmus responded to transmural stimulation with a single maintained response. This response was abolished by phentolamine, guanethidine, tetradotoxin and 6-hydroxydopamine showing that it resulted from the release of noradrenaline from adrenergic nerves and an action on alpha receptors. Propranolol had no effect on the responses of circular isthmic muscle suggesting that the beta receptors were relatively unimportant in determining the magnitude of the response. Cocaine failed to potentiate the magnitude of the response to field stimulation but did prolong the duration of the response. UO521, an inhibitor of COMT, had no effect on the responses of circular isthmus to transmural.

Animals↗
PubMedDate not supplied

Pituitary and testicular function in spontaneously hypertensive rats.

Levels of plasma gonadotropins, prolactin (PRL), and testosterone, and the testicular concentration, total content, and affinity of hCG binding sites were measured in male spontaneously hypertensive rats (SHR) and in genetically matched normotensive (WKY) rats. Hypertensive rats had higher plasma PRL and FSH levels and lower plasma testosterone levels. The affinity of testicular hCG binding sites was similar in SHR and WKY rats, but SHR had considerably lower concentration and total content of hCG-binding sites than did WKY animals. The comparison of these findings with those obtained previously with pituitary-grafted rats and with tumor-bearing rats indicates that the endocrine effects of hyperprolactinemia may vary depending on the rate and magnitude of the increase in peripheral PRL levels. Species differences in the response to hyperprolactinemia and differences between SHR and other rat strains suggest that hormonal responses to PRL elevation depend also on the genetic characteristics of the animal.

Animals↗
PubMedDate not supplied

Testicular LH receptors during aging in Fisher 344 rats.

Levels of serum LH, prolactin, testosterone, progesterone and 17-OH progesterone and the testicular concentration and total content of LH receptors were measured in 4-, 11-, 18-, and 27-month-old Fisher 344 rats. All 27-month-old rats had Leydig cell tumors. At first, testicular LH receptor levels decreased with age, but with the appearance of the testicular tumors, these levels increased dramatically. Serum prolactin levels fluctuated with age, but were significantly decreased in 27-month-old rats, as were serum LH levels. Serum testosterone levels decreased steadily with age, while the testosterone-LH receptor ratio remained constant until the appearance of the testicular tumors, after which the ratio decreased precipitously. Serum progesterone levels remained constant throughout the life of Fisher 344 rats until the appearance of testicular tumors, when they increased dramatically. Serum 17-OH progesterone levels were increased significantly at 11 and 27 months as compared to four months of age, but levels at 18 months were similar to those seen in the 4-month-old animals. Therefore, in aged Fisher 344 rats with spontaneous Leydig cell tumors, there is an alteration in the testicular testosterone synthesizing pathway at a step after progesterone.

17-alpha-Hydroxyprogesterone↗
PubMedDate not supplied

Evidence-based prevention of post-operative adhesions.

Despite decades of research, numerous new product ideas and 'carefully considered opinions' of recognized experts, very few products for the prevention of post-operative adhesions have met the requirements for Level 1 evidence of safety and efficacy. Those that have are useable only at laparotomy. Several new liquid products intended for use at laparoscopy are in various stages of development and clinical investigation. Hopefully, some will prove to be both simple to use and efficacious. Even if this occurs, it must be remembered that a reduction in post-operative adhesions does not necessarily produce a better clinical outcome. Our common sense suggests that fewer adhesions should logically result in less pain, more pregnancies, fewer bowel obstructions and less long-term morbidity. We believe that 'fewer adhesions' is a good thing, but we have no controlled human trials to prove this. How much of a reduction in post-operative adhesions is necessary before it is clinically relevant? A single adhesion in the wrong anatomic location may be catastrophic. How do we measure this? Until these and other questions have been answered (if ever), we have nothing more than educated guesses that all these efforts are warranted.

Biocompatible Materials↗
PubMedDate not supplied

Effect of age on responsiveness of isolated rat atria to carbachol and on binding characteristics of atrial muscarinic receptors.

Inotropic and chronotropic responses to carbachol were studied in isolated, electrically driven left atria and in spontaneously beating right atria from 6-month-old (adult) and 25-month-old (senescent) rats. The inotropic, but not the chronotropic, response to carbachol was reduced in the senescent animals. However, the inotropic response to nifedipine was not significantly different in the two groups. Likewise, the number (Bmax) and affinities of binding sites for the muscarinic antagonist [3H]quinuclidinyl benzylate (Kd) and for the muscarinic agonist carbachol (Ki) did not change with age. The reduced responsiveness to the inotropic effect of carbachol in senescent animals may result from alteration in events distal to the muscarinic receptor and proximal to Ca2+ transport.

Aging↗
PubMedDate not supplied

Overview of bone marrow and stem cell transplantation.

Bone marrow transplants and peripheral blood mononuclear cell transplants have improved survival of many patients with hematologic malignancies. This aggressive approach uses high-dose chemotherapy and radiation therapy for acute and chronic leukemia, lymphoma, Hodgkin's disease, multiple myeloma, and selected solid tumors. High-dose therapy requires intensive medical and nursing care. The focus of care is the management of side effects, monitoring of toxicities, and prevention of complications. The outcome of bone marrow and peripheral cell transplants is related to patient age, underlying disease status, and type of transplant.

Bone Marrow Transplantation↗