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L Hyland

Publications and source records attributed to L Hyland.

32 records · Page 2Linked to original sources
PubMed1985

Further examination of the inhibitory actions of alpha 1-adrenoceptor agonists in rat vas deferens.

The inhibitory actions of alpha 1-adrenoceptor agonists were examined in the isolated bisected vas deferens of the rat. The calcium entry facilitator Bay K 8644 markedly potentiated the isometric contraction to a single stimulus pulse in epididymal portions of rat vas deferens: subsequent amidephrine produced an inhibition which was antagonised by the alpha 1-adrenoceptor antagonist, prazosin, but not by the alpha 2-adrenoceptor antagonist, yohimbine. The alpha 1-adrenoceptor agonists amidephrine and cirazoline failed to inhibit the transmitter overflow to trains of pulses at a frequency of 2 Hz in epididymal portions, but also failed to abolish the nifedipine-resistant adrenergic contraction to trains of pulses at 2 Hz in epididymal portions. It is concluded that alpha 1-adrenoceptor agonists have inhibitory effects which may be by action at presynaptic alpha 1-adrenoceptors.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Further examination of the effects of ageing on the adrenoceptor responsiveness of the rat vas deferens.

Age-related changes in presynaptic alpha 2-adrenoceptors were investigated in prostatic and epididymal portions of vasa deferentia from young adult (2-3 months) and old (24-29 months) Sprague-Dawley rats, using the alpha 2-selective agonists xylazine and clonidine. In prostatic portions the inhibitory effects of clonidine against the isometric contractions to single pulse field stimulation were complicated by a postsynaptic action in old animals, but in epididymal portions in the presence of nifedipine both xylazine and clonidine were 3 times less potent in old rats. However, there were no significant differences between young and old in the potency of xylazine at inhibiting the overflow of tritium or the isometric contraction evoked by 5 Hz stimulation for 3 min in tissues pre-incubated with [3H]noradrenaline. It is suggested that there is reduced responsiveness of presynaptic alpha 2-adrenoceptors in the vas deferens of old rats, but that this can only be demonstrated using a sensitive measure of the presynaptic potency of agonists: the isometric contraction to a single stimulus.

Aging↗
PubMed1985

Vascular alpha 2-adrenoceptors can mediate nerve stimulation-evoked contractions.

It is now established that alpha 2-adrenoceptors can be present on vascular smooth muscle as targets for exogenous agonists, but some controversy exists as to whether these vascular alpha 2-receptors may also be the target for neurally released noradrenaline. In human saphenous vein we have found evidence that the alpha 2-antagonist yohimbine in low concentrations (0.01 mumol/l) can significantly inhibit stimulation-evoked contractions, whereas the alpha 1-antagonist prazosin is more than ten times less potent. It is concluded that, at least in some tissues, neuro-effector transmission can be mediated by vascular alpha 2-adrenoceptors.

Adrenergic alpha-Antagonists↗
PubMed1985

No evidence for differences between pre- and post-junctional alpha 2-adrenoceptors.

We have examined the pre- and post-junctional effects of a series of alpha-adrenoceptor agonists and antagonists at alpha 2-adrenoceptors in the pithed rat preparation and the human isolated saphenous vein. In the pithed rat, there was no difference in relative agonist and antagonist potencies between pre- and post-junctional alpha 2-adrenoceptors but the absolute potencies of antagonists differed: antagonists were more potent prejunctionally. In the human saphenous vein, the alpha 2-adrenoceptor antagonist yohimbine had pre- and post-junctional actions over the same concentration range. We have no evidence to suggest differences between pre- and post-junctional alpha 2-adrenoceptors: differences in absolute antagonist potencies in the pithed rat may be due to non-equilibrium conditions.

Adrenergic alpha-Agonists↗
PubMed1985

Evidence for neuro-effector transmission through postjunctional alpha 2-adrenoceptors in human saphenous vein.

The effects of the alpha 1-adrenoceptor antagonist prazosin and the alpha 2-adrenoceptor antagonist yohimbine were examined against stimulation-evoked contractions in human isolated saphenous veins. The concentration of yohimbine producing 30% inhibition of stimulation-evoked contractions (IC30) was 13.2 nM, whereas the IC30 of prazosin was greater than 250 nM. The inhibition of stimulation-evoked contractions by yohimbine was not prejunctionally mediated since yohimbine (0.01-0.1 microM) significantly potentiated the stimulation-evoked overflow of tritium in tissues pre-incubated with [3H]-noradrenaline. The high potency of yohimbine and the low potency of prazosin indicate that neuro-effector transmission in human saphenous vein is mediated predominantly by postjunctional alpha 2-adrenoceptors.

Adult↗
PubMed1984

An investigation of the actions of the calcium entry facilitator Bay K 8644 on the rat vas deferens.

The pre- and postsynaptic actions of the calcium entry facilitator Bay K 8644 were investigated in the rat isolated vas deferens. Bay K 8644 had no presynaptic effect on adrenergic neurotransmission in the epididymal portion. Bay K 8644 and alpha 1-adrenoceptor agonists potentiated, and the calcium entry blocker nifedipine abolished, the non-adrenergic contraction to a single stimulus in prostatic portions. Bay K 8644 sensitised the prostatic portion to, but did not increase the maximum height of, spontaneous direct contractions produced by alpha-agonists.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1984

Production of all follicle-stimulating hormone isohormones from a purified preparation by neuraminidase digestion.

Graded removal of sialic acid residues from a purified preparation of rat follicle-stimulating hormone (FSH; NIADDK-FSH-I-5) by neuraminidase digestion resulted in the production of FSH isohormones with isoelectric points identical to those found within pituitary tissue. In addition, each neuraminidase-produced FSH form exhibited a radioreceptor assay:radioimmunoassay ratio similar to that of its endogenously produced counterpart. Thus, the molecular basis for FSH microheterogeneity appears to be due to the varying degree of sialylation into a common FSH protein core. We have demonstrated that the pituitary gland produces different amounts of these FSH isohormones depending upon the surrounding endocrine environment. The results of the present studies suggest the existence of biochemical mechanisms within the pituitary that influence sialic acid incorporation into FSH. These mechanisms appear to be sensitive to the surrounding hormonal milieu and serve to alter the intensity of the FSH stimulus delivered to the gonad.

Animals↗
PubMed1984

Regulation of the pulsatile releases of luteinizing and follicle-stimulating hormones in ovariectomized hamsters.

We have combined for modifications of common radioimmunoassay (RIA) techniques to increase the sensitivity of the gonadotropin assays by an order of magnitude compared with those generated according to the instructions provided by the National Pituitary Agency. The four modifications are: a) enzymatic radioiodination, b) purification of radiolabeled hormones by Sephadex and concanavalin A chromatography, c) reduced first antibody concentration, and d) a prolonged incubation time. These methods increase the sensitivities of the RIAs and allow for the quantitation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in small volumes of plasma. We have used these methods to measure the changes in pulse frequency and amplitude of LH and FSH in ovariectomized hamsters after a variety of neuroendocrine manipulations. Alterations in catecholaminergic neurotransmission affect the frequency and amplitude of LH but not FSH release, and suggest that the hypothalamic mechanisms responsible for LH releasing hormone (LHRH)-mediated LH release are distinct from those that regulate FSH secretion. Further, alterations in LHRH-pituitary interactions (elicited by injections of LHRH antisera or a potent LHRH agonist), suggest the existence of separate control mechanisms responsible for LH and FSH release at the level of the adenohypophysis. Combined, these studies provide further evidence for complex and separate neuroendocrine regulatory control over the secretion of each gonadotropin.

Animals↗
PubMed1984

Autoregulation of follicle-stimulating hormone secretion in the hamster: evidence for control at the level of the anterior pituitary gland.

Pituitary tissue obtained from proestrous, phenobarbital-treated hamsters was placed in organ culture, and the release rates of FSH and LH were monitored. Addition of LHRH to the culture medium increased gonadotropin release rates. Preincubation of pituitaries in medium that contained 1 microgram purified FSH ( NIADDK rat FSH-I-5) resulted in enhanced basal and LHRH-induced FSH release rates. Full expression of FSH hypersecretion by pituitary tissue occurred after 3-h exposure to purified FSH. This phenomenon appears to require adequate tissue calcium concentrations. Further, exposure of pituitaries to purified FSH slightly but significantly enhanced basal but not LHRH-stimulated LH release compared with that in untreated controls. Experiments that employed labeled FSH, reduced exposure time to purified FSH, or decreased calcium concentration in the medium proved that the increased FSH secretory rate was not due to contamination of the medium with the purified FSH used to stimulate the pituitary. These studies suggest that FSH has the ability to influence its own secretion by an action at the level of the anterior pituitary gland.

Animals↗
PubMed1983

Pituitary follicle-stimulating hormone heterogeneity: assessment of biologic activities of each follicle-stimulating hormone form.

The multiple species of follicle-stimulating hormone (FSH) present within pituitary tissue were separated by the technique of polyacrylamide gel isoelectric focusing. The ability of each FSH species to stimulate the secretion of plasminogen activator from cultured granulosa cells was tested (FSH in vitro bioassay). A wide range of biologic/radioimmunologic FSH activity was observed when FSH species were compared. As the isoelectric point of the FSH molecule declined, so did the biologic activity. A second series of studies was performed to determine which forms of FSH were secreted by pituitary tissue in vitro. All of the forms of FSH present in pituitary tissue were secreted into culture medium. However, the relative proportions of FSH forms in the pituitary and medium were not always similar. Exposure of pituitary tissue to luteinizing hormone-releasing hormone elicited an increase in the relative proportion of the more biologically active forms of FSH that were secreted. These studies suggest that the hormonal milieu surrounding the pituitary affects not only the quantity but also the potency of the FSH signal emitted. Thus, the basis for observed differences between biologic and immunologic FSH activities observed during some endocrine states may be the result of preferential secretion of certain FSH species.

Animals↗
PubMed1976

The axillo-axillary bypass graft: further experience.

The recent utilization of the axillo-axillary bypass graft for revascularization of proximal subclavian or innominate artery occlusions has proved to be a successful operation, technically simple with a low operative morbidity. We have reviewed the reported experience to date and have added our experience of nine additional cases. The procedure has produced excellent results in all patients, with no evidence of postoperative "steal" from the donor limb. Preoperative hemodynamic defects were corrected. Our experience has led us to the conclusion that this simpler and safer extrathoracic approach should be considered as the procedure of choice when arterial lesions allow for its selection and use.

Adult↗
PubMedDate not supplied

Oxygenating mouthguard alleviates hypoxia during gastroscopy.

A randomized study was carried out to determine the effect of oxygen (3 liters/min) via a novel oxygenating mouthguard (Oxyguard) on arterial oxygenation in 242 intravenously sedated patients undergoing gastroscopy. In another group of 21 patients, a randomized crossover study of arterial oxygen saturation using either the standard mouthguard or the oxygenating mouthguard (3 liters/min) was conducted. Significant O2 desaturation (pulse oximeter reading less than 90%) occurred in 25% of patients on room air but only 3% of those on oxygen (p less than 0.001). Severe desaturation (reading less than 85%) occurred in 5% of patients on room air but was prevented by the oxygenating mouthguard. Minimum oxygen saturation levels were significantly higher in patients on oxygen (90.5 +/- 0.3%) than on air (86.5 +/- 0.5%; p less than 0.001). In the crossover group, O2 saturation was uniformly higher in the recordings of all patients using the oxygenating mouthguard. In conclusion, administration of oxygen via the oxygenating mouthguard alleviates hypoxemia during gastroscopy and prevents severe oxygen desaturation. However, hypoxemia may occur even during use of supplemental oxygen. Hence, monitoring of arterial oxygenation is recommended.

Equipment Design↗
PubMedDate not supplied

ALARA study of teaching effectiveness on reducing radiation exposure.

The purpose of this study was to measure the effectiveness of radiation safety instruction and the impact on radiation film badge levels. A convenience sample of 144 endoscopy nurses and technicians was pretested for radiation safety knowledge, given a course in radiation safety, and then posttested immediately after the course and then 6 months later. Radiation badges were analyzed for radiation exposure at preinstruction, 1 month postinstruction, and 6 months postinstruction. Results showed that the instruction was effective. There was only a slight decrease in radiation badge readings; the decrease, however, was not statistically significant.

Adult↗