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Biomedical subjects

P K Opstad

Publications and source records attributed to P K Opstad.

At least 19 recordsLinked to original sources
PubMed1992

Androgenic hormones during prolonged physical stress, sleep, and energy deficiency.

Androgenic hormones were investigated during two separate 5-day military endurance training courses, with physical activities around the clock corresponding to a daily energy consumption of about 40,000 kilojoules, but with an intake of only 2,000 kilojoules. Altogether, the cadets slept for 1-3 h in the 5 days. Eleven male cadets participated in course I, and 10 in course II. Plasma levels of testosterone, free testosterone, dehydroepiandrosterone, 17 alpha-hydroxyprogesterone, and androstenedione decreased by 60-80% during the course. In contrast, plasma cortisol, aldosterone, progesterone, and dehydroepiandrosterone sulfate increased. LH, FSH, and ACTH decreased to about 50-80% of precourse levels. Weak correlations between plasma levels of hypophyseal and levels of adrenal and testicular hormones indicate a multifactorial regulation. In conclusion, both adrenal and testicular androgens decrease during prolonged physical strain combined with energy and sleep deficiency.

Adrenocorticotropic Hormone↗
PubMed1992

The hypothalamo-pituitary regulation of androgen secretion in young men after prolonged physical stress combined with energy and sleep deprivation.

During a five days' military training course for male cadets with hard physical activity day and night and almost no sleep or food, a decrease was found in LH, FSH, PRL and TSH. A decrease was also found in testosterone, dihydrotestosterone (DHT), androstenedione, dehydroepiandrosterone and 17 alpha-OH progesterone, whereas dehydroepiandrosterone-sulfate increased twofold. The LH and FSH responses to GnRH intravenously were increased at the end of the course. This demonstrates enhanced pituitary reserves of gonadotropin, or, alternatively, increased sensitivity to GnRH stimulation and may be due to decreased hypothalamic secretion of GnRH during the course. The decreased DHT and testosterone levels were almost normalized after HCG stimulation, indicating a gonadotropin regulated decrease in testosterone secretion during the course. In spite of fairly weak correlation between the alteration in gonadotropins and androgens it is concluded that there is a major regulation of testicular androgen secretion during prolonged stress by the hypothalamo-pituitary axis.

Adult↗
PubMed1992

Changes in the gastrointestinal mucosa after long-distance running.

Two groups of long-distance runners were investigated for the effect of marathon running on the gastrointestinal mucosa. In one group gastric erosions with bleeding were found in five of nine subjects, mostly localized to the corpus region. The relative gastric blood flow measured by endoscopic laser Doppler flowmetry was slightly decreased in the cardia region (from 7.0 to 5.8; p less than 0.05) but unchanged in the other parts of the stomach, including the erosive lesions. In another group (n = 8) all the subjects showed a substantial increase in the urinary excretion of 51Cr-labeled ethylenediaminetetraacetic acid after oral intake, which indicates an increase in the intestinal permeability. There is reason to suggest that long-distance running affects the integrity of the gastric and the intestinal mucosa.

Adult↗
PubMed1991

Strenuous prolonged exercise elevates resting metabolic rate and causes reduced mechanical efficiency.

Resting O2 consumption, net mechanical efficiency during cycling exercise and excess postexercise O2 consumption (EPOC) was measured in 15 army cadets after 3 or 4 days of continuous simulated combat exercises (estimated energy demand: 40 MJ day-1), no organized sleep and virtually no food intake (stress experiment). They exercised for 30 minutes at a work load corresponding to about 50% of maximal O2 uptake. An identical test using the same absolute work load was repeated when the cadets were completely recovered from the combat course (control experiment). Resting O2 consumption increased by 15% from 279 +/- 7 ml min-1 (control) to 320 +/- 8 ml min-1 (stress, P less than 0.001). Mechanical efficiency decreased from 24.6 +/- 0.4% (control) to 20.9 +/- 0.2% (stress, P less than 0.001). EPOC1h increased from 0.58 +/- 0.41 l (control) to 2.24 +/- 0.2% (stress, P less than 0.05). Glucose infusion during exercise (0.20 g kg-1 body weight) had no effect on mechanical efficiency or EPOC. About 1/5 of the increase in exercise O2 uptake can be explained by a substrate shift from carbohydrates to fat, as evidenced by a reduction in R-value during exercise from 0.90 +/- 0.012 (control) to 0.80 +/- 0.010 (stress). Hence, after severe physical stress combined with sleep deprivation and food restriction, O2 uptake is increased both at rest and during submaximal exercise.

Adult↗
PubMed1991

Alterations in the morning plasma levels of hormones and the endocrine responses to bicycle exercise during prolonged strain. The significance of energy and sleep deprivation.

The relative significance of physical exercise, energy and sleep deprivation for the morning levels of hormones and the endocrine response to short-term bicycle exercise were investigated in 24 male cadets during a 5-day military training course. Significant increases in the morning levels of noradrenaline, adrenaline, and dopamine, and a decrease in PRL were ascribed mainly to physical strain. Cortisol and hGH increased, whereas insulin and glucose decreased mainly due to energy deficiency. Pulse rate after the bicycle test was unchanged and similar in all groups in spite of increased catecholamine responses. The increased catecholamine response was mainly due to physical strain. The cortisol response to the bicycle test was increased in all groups, and energy deficiency caused slower postexercise recovery. The incremental hGH response to the exercise test was unchanged in the energy-deficient subjects but abolished in the well-fed subjects. The results suggest that the endocrine responses during long-lasting exhausting strain were mainly due to physical exertion and energy deficiency, whereas sleep deprivation did not play any major role.

Adult↗
PubMed1991

Reduced set-point temperature in young men after prolonged strenuous exercise combined with sleep and energy deficiency.

The effects on body temperature of 3-4 days of continuous military exercise combined with energy and sleep deficiency, at rest and in response to an exercise test (45% of VO2max for 30 min) and the following recovery, have been studied in fifteen young male cadets. During the course, at rest before exercise, rectal temperature was reduced by 0.57 +/- 0.15 degrees C, whereas trunk temperature was increased by 1.47 +/- 0.50 degrees C, and thigh temperature by 2.69 +/- 0.64 degrees C. Oxygen uptake increased 14-24% both before and during the exercise test in the stress experiment. During the course slightly lower rectal temperature levels were seen during the exercise test, whereas skin temperatures were significantly increased. Since the cadets' heat production and loss appeared to be increased and core temperature reduced, it is possible that we have observed a lowered set-point for core temperature.

Adult↗
PubMed1990

Transcutaneous nerve stimulation in patients with coronary arterial disease: haemodynamic and biochemical effects.

Low-frequency transcutaneous nerve stimulation (TNS) is known to produce widespread and prolonged vasodilation in skin and muscles. In the present study the effects of low-frequency TNS on coronary and systemic haemodynamics, myocardial blood flow, myocardial oxygen consumption, myocardial free fatty acid and lactate uptake were measured at rest in 16 normotensive patients, with coronary heart disease, undergoing diagnostic cardiac catheterization. In addition, vasoactive intestinal polypeptides (VIP) and noradrenaline were measured in the coronary sinus and the aorta. The study was randomized and double-blind, with half of the patients serving as placebo controls. A stimulation period of 20 min caused a significant lowering of mean femoral arterial pressure and systemic vascular resistance measured at 15 and 30 min after the start of TNS (P less than 0.01). There was no significant change in the other parameters mentioned. The hypotonic effect is considered to be due to increased peripheral microcirculation resulting from sympatho-inhibition.

Coronary Circulation↗
PubMed1989

Elevated VIP and endotoxin plasma levels in human gram-negative septic shock.

Vasoactive intestinal polypeptide (VIP) and endotoxin (lipopolysaccharides, LPS) were measured in plasma samples from 11 patients with bacteriologically verified meningococcal disease. Five patients suffered fulminant septicaemia, developed severe septic shock, and 2 died due to circulatory collapse. Initially, all 5 had levels of VIP above 4 pM and plasma endotoxin above 200 ng/liter. Five patients were diagnosed as meningitis and 1 as having meningococcaemia, all with a normal circulatory state. None of these 6 patients had initially levels of VIP above 2.5 pM or endotoxin levels above 25 ng/liter (P less than 0.001). A correlation existed between plasma endotoxin and VIP levels (r = 0.735, P = 0.01). Sequentially collected samples from 3 patients showed rapidly declining VIP levels after initiation of antibiotic and fluid treatment. These results are in agreement with previous animal experiments, suggesting that endotoxin directly or indirectly stimulates the VIP-ergic nervous system in the initial phase of gram-negative septic shock in man.

Adult↗
PubMed1989

Adrenaline-mediated glycogenolysis in different skeletal muscle fibre types in the anaesthetized rat.

The effect of adrenaline infusion on glycogen breakdown in different muscle fibres types in resting extensor digitorum longus (EDL) and soleus was investigated with histochemical methods. During adrenaline infusion the glycogen content in type IIB and type IIA fibres in EDL, as measured in PAS-stained sections, decreased 24.5% and 11.5% respectively. The glycogen content in type I fibres in EDL and in type I, type IIA and T-fibres in soleus did not change during adrenaline infusion. The present study shows that adrenaline infusion has different effects on glycogen breakdown in the different fibre types in EDL and a different effect on type IIA fibres in EDL and soleus. So far, the reason for these differences is unknown.

Animals↗
PubMed1989

Erosive prepyloric changes--a manifestation of stress?

To study the relationship between stress and the endoscopic diagnosis of erosive prepyloric changes (EPC), upper gastrointestinal endoscopy was performed twice in 19 cadets from the Military Academy, once in a 'non-stressed' situation and once after exposure to a standardized stress model. Five biopsy specimens per examination were obtained from the prepyloric mucosa, and the features of acute and chronic inflammation, erosion, and campylobacter-like structures (CLS) were evaluated. The endoscopy showed a significant (p less than 0.001) aggravation of EPC after stress. The histologic examination showed an increase of acute inflammation (p less than 0.05) and a higher density of CLS (p less than 0.01) after stress, as compared with the findings under non-stressed conditions. No association was observed between CLS and EPC. The study sheds new light on the pathogenesis of EPC, as it shows that EPC is aggravated during stress.

Adult↗
PubMed1989

Reduced systolic blood pressure elevations during maximum exercise at simulated altitudes.

Ten healthy female subjects performed maximum exercise on a bicycle in an altitude chamber during normoxia and hypobaric hypoxia simulating altitudes of 2,450, 3,700 and 4,600 m. The increases in systolic blood pressure responses were reduced with the degree of hypobaric hypoxia, whereas heart rate and diastolic pressure responses were unchanged. The increases in blood levels of aldosterone, plasma renin activity, adrenaline, noradrenaline, neuropeptide-Y and vasoactive intestinal peptide were similar at the different simulated altitudes. Angiotensin-converting enzyme and vasoactive intestinal peptide levels were not affected by hypoxia or maximum exercise. The present results suggest that the decreases in systolic blood pressure responses during hypobaric hypoxia could not be explained by altered responses of the measured vasoactive substances from the renin-angiotensin, gastrointestinal, and autonomic nervous systems.

Adult↗
PubMed1988

The influence of prolonged physical stress on gastric juice components in healthy man.

Eight healthy men were exposed to 5 days of continuous heavy exercise combined with caloric deficiency and sleep deprivation. Immediately after the stress period the fasting and postprandial intragastric bile acid concentration, pepsin concentration, and gastric juice acidity were measured. Compared with a control experiment performed 8 weeks later, the results from the stress period showed a sevenfold increase in the fasting concentration of intragastic bile acids (from 35 mumol/l to 256 mumol/l; p less than 0.02), there was a tendency towards an increase in the fasting intragastric pepsin concentration, and there was an increase (p less than 0.05) in the intragastric pH level throughout the 3rd postprandial hour. It appears that physical stress induces changes in the intragastric milieu that might dispose for mucosal lesions.

Adult↗
PubMed1987

Comparison of VIP and beta 2-adrenoceptor-induced relaxations in the circular and longitudinal smooth muscle layers of the rat portal vein.

The relative importance of VIP in reduction of vascular tone was studied in circular and longitudinal preparations of the VIP-innervated rat portal vein. Exogenous VIP inhibited the methoxamine-evoked contractures in the atropine-blocked preparations with a lower potency in the inner, circular (pD2 = 6.4 +/- 0.5, n = 6) than in the outer, longitudinal layer (pD2 = 7.7 +/- 0.1, n = 6). VIP was also a less efficient relaxant (intrinsic activity (alpha) = 0.60 +/- 0.16, n = 6) of the inner than of the outer layer (alpha = 1.00). The selective (salbutamol) and the non-selective (isoproterenol) beta 2-agonists completely relaxed the methoxamine contractures in both layers and the potency (isoproterenol) was higher in the inner (pD2 = 6.39 +/- 0.32, n = 6) than in the outer layer (pD2 = 5.67 +/- 0.34, n = 6). Plasma from the portal-mesenteric vein of anaesthetized, fasting rats contained 0.036 nM VIP (median, n = 17), that is, several orders of magnitude lower than the range of VIP concentrations relaxing the methoxamine contracted vein preparations via VIP receptors of the apamin-blockable category. The results support the hypothesis that alpha 1-adrenoceptor-induced contractions in the circular layer are predominately relaxed via beta 2-adrenoceptors while relaxation of the outer layer may occur via VIP receptors, probably activated by local release of the neuropeptide.

Albuterol↗
PubMed1987

Binding and degradation of vasoactive intestinal peptide in prolactin-producing cultured rat pituitary tumour cells (GH4C1).

Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion from cultured rat pituitary cells (GH cells) (Bjøro et al. 1984). This study demonstrates the presence of specific receptors for 125I-VIP on the GH4C1 cells. Specific binding was rapid and biphasic giving a transient plateau lasting from 7 to 30 min. Thereafter specific binding declined to about one-third after 90 min. This coincided with enhanced degradation of 125I-VIP. The degradation was mainly cell-mediated and only partly receptor dependent. Trichloroacetic acid precipitation and absorption chromatography indicated that the degradation products were either 125I- and/or small labelled peptide fragments. Bioassay, RIA and rebinding studies also demonstrated degradation of VIP. Pretreatment of GH4C1 cells with trypsin decreased the rate of degradation of 125I-VIP, but also reduced the amount of specific binding. Scatchard analysis of binding data indicated the existence of two independent classes of receptors, one with Kd = 2.2 nM and Bmax = 15 fmol per 10(6) cells and another with Kd = 180 nM and Bmax = 550 fmol per 10(6) cells. The IC50 for VIP, PHI and secretin were 4, 5 and 500 nM, respectively. We conclude that the high affinity receptor is the most probable mediator of VIP on PRL secretion. The effect of VIP and PHI on PRL secretion in GH4C1 cells is mediated through one common receptor.

Animals↗
PubMed1986

Biochemical plasticity in the superior colliculus of adult rats after chronic visual cortex ablation.

We have measured the changes of several neurochemical parameters in the adult rat superior colliculus (SC) 1.5-4 months after unilateral visual cortex ablation. High-affinity uptake of D-[3H]Asp was increased by 22.5% and glutamate decarboxylase by 10% in the ipsilateral SC. This may be largely attributed to reactive synaptogenesis of intrinsic glutamatergic and GABAergic neurons, respectively. The noradrenaline content was increased by about 60 and 25% in the ipsi- and contralateral SCs, respectively. The latter probably reflects sprouting of noradrenergic fibres from the locus coeruleus.

Afferent Pathways↗
PubMed1986

Increase in plasma vasoactive intestinal polypeptide (VIP) in muscular exercise in humans.

We have previously shown that plasma vasoactive intestinal polypeptide (VIP) is increased in normal subjects by low-frequency transcutaneous nerve stimulation. The latter may also increase short-term physical performance in athletes (running, swimming and ergometer cycling). The present study examines whether the plasma VIP level is similarly increased in short-term ergometer exercise in seven healthy volunteers. A group of four patients with angina pectoris were included, since a lowered concentration of VIP is found in diseased heart tissue. In the group of healthy subjects, ergometer exercises with progressive increases in workload until exhaustion, lasting from 16 to 32 min (mean 26 min) and with a corresponding maximum energy output of 1500 to 5100 W (mean 3560 W), resulted in an increase in plasma VIP concentration from a pre-stimulatory level of 3.3 pmol . l-1 to 5.3, 5.2 and 5.6 pmol . l-1, measured 3, 10 and 20 min respectively, following termination of the exercise, i.e. a maximal 70% increase. In the patients with angina pectoris there was no significant VIP increase (cycling time 7-15 min, work performed 400-1350 W). Possible triggering mechanisms for VIP release and its source are discussed.

Adult↗
PubMed1985

Plasma renin activity and serum aldosterone during prolonged physical strain. The significance of sleep and energy deprivation.

Plasma renin activity (PRA), serum aldosterone and the serum and urinary levels of sodium and potassium have been investigated in 24 young men participating in a 5-day military training course with heavy continuous physical exercise, energy and sleep deprivation. The subjects were divided into three groups. Group 1 did not get any extra sleep or food, group 2 were compensated for the energy deficiency, and group 3 slept 3 h each night. The basic diet given to all the subjects was about 5,000 kJ and 2 g NaCl X 24 h-1 X cadet-1. The high calorie diet contained approximately 25,000-35,000 kJ and 20 g of NaCl X 24 h-1 X cadet-1. The study showed that serum aldosterone and PRA were extremely activated during such prolonged physical strain combined with lack of food and salt, whereas sleep deprivation did not seem to have any large influence. Only small variations were found in the serum levels of sodium and potassium and the urinary level of potassium during the course, whereas a decrease was seen in urinary sodium concentration. The fairly good correlations between the decrease in urinary sodium levels and the increase in PRA (r = 0.7) and further between PRA and serum aldosterone (r = 0.8) during the course indicate that there is a causal connection between the decrease in urinary sodium excretion and the increase in PRA and serum aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗