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Biomedical subjects

J J Theron

Publications and source records attributed to J J Theron.

At least 19 recordsLinked to original sources
PubMed1992

Putative melatonin receptor in human spermatozoa.

Melatonin is present in human semen, and may affect sperm motility. The presence of melatonin receptors on spermatozoa has not yet been reported. Detection of melatonin-binding sites may be limited because of the masking of such sites by sialic acid. Spermatozoa were obtained from eligible human donors, incubated with neuraminidase to remove sialic acid residues, and saturation binding assays were carried out using 2-125I-melatonin as a receptor probe. Consistent 125I-melatonin binding could only be obtained after spermatozoa were treated with neuraminidase. Scatchard analysis revealed a low-affinity binding site (ML-2) with a Kd value of 127 +/- 6 nM and a Bmax of 25 +/- 4.5 fmol/mg protein. These results present evidence of melatonin-binding sites in spermatozoa. Sialic acid possibly regulates the binding of melatonin to these sites.

Adult↗
PubMed1989

Consecutive melatonin circadian rhythms in normal volunteers.

Circadian plasma melatonin secretion patterns were determined in 12 healthy men over 3 consecutive 24-hour periods. The rhythms showed marked intra-individual stability, but pronounced interindividual variation. Plasma melatonin may serve as a reliable biological marker. Plasma melatonin assayed between 23h00 and 01h00 gave a reliable indication of an individual's circadian melatonin rhythm.

Adult↗
PubMed1988

The pineal organ in man. An endocrine gland awaiting recognition.

Information on pineal gland function in man is briefly reviewed. The evidence presented suggests that in man the pineal gland: (i) is involved in control of certain types of behaviour, such as sleep and sleepiness; (ii) is associated with direction orientation; (iii) is in some way related to the phenomenon known as jet lag; (iv) affects sexual maturation; and (v) may affect sperm motility. On the basis of available evidence it is concluded that in man the pineal gland must be regarded as an endocrine gland participating in the close synchronization of a variety of functions.

Adolescent↗
PubMed1985

Cardiac substances that influence blood-pressure. II. Potent pressor activity in rat and rabbit atrial muscle.

In addition to their natriuretic, diuretic and vasodilator activities, freshly prepared aqueous extracts of either rat or rabbit atrial myocardium were shown to elicit significant increases in the blood-pressure of anaesthetized rats. Small aliquots (0.05 ml) intravenously administered caused a transient rise in mean arterial blood-pressure of up to 20%. Slow infusion of 0.4 ml right atrial extract (corresponding to about one half of a rabbit right atrial lobe) during 90 seconds caused the expected natriuresis and diuresis, together with a sustained elevation in arterial blood-pressure (ca 25%) that returned to normal within 3 minutes. This potent pressor activity could not be detected in ventricular extracts. It was furthermore readily separable from the natriuretic peptides and catecholamines by ultrafiltration. The atrial pressor factor is a small proteolytically unstable molecule (300-1000 dalton).

Animals↗
PubMed1985

Effect of chlorpromazine on the localization of cAMP phosphodiesterase.

Chlorpromazine (CPZ) at dosages of 10 mg/kg body weight (b.wt.) affected the cytochemical localization of cAMP-dependent phosphodiesterase (cAMP PDE) activity in the synapses of the rat frontal cortex. Postsynaptic cAMP PDE activity was inhibited, and presynaptic activity increased. CPZ also inhibited membrane-bound ATPase activity in the frontal cortex. The activity of Na+-K+-ATPase was significantly (P less than 0.005) inhibited in isolated plasma membranes from the rat frontal cortex. CPZ exposure also affected the cytochemical localization of cations with potassium pyroantimonate. Precipitate, which could be removed with 5 mm EGTA, was decreased in the mitochondria and synaptic vesicles in presynaptic areas after CPZ treatment. The incorporation of 45Ca2+ into slices of the rat frontal cortex was also significantly (P less than 0.001) inhibited by CPZ. This ultrastructural study shows that CPZ may affect biochemical events in an opposite manner in the pre- and post-synaptic areas of some neurons of the frontal cortex.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1979

Microfilaments, the smooth endoplasmic reticulum and synaptic ribbon fields in the pinealocytes of the baboon (Papio ursinus).

Microfilaments (MF, 5-8 nm in diameter) are a prominent feature of the pinealocyte cytoplasm of baboons (Papio ursinus) kept under controlled lighting conditions. MF occurred as a filamentous network in these cells during the light phase of the diurnal light-dark cycle, while a close structural association was noted between MF and the membranes of the smooth endoplasmic reticulum (SER). This association was especially evident during the dark period. Increased numbers of single synaptic ribbons (SR, vesicle-crowned rodlets), together with large aggregations of SR, i.e., ribbon fields (RF), were seen in the pinealocyte cytoplasm of baboons killed during the dark phase. It is suggested that the vesicles of RF may arise from those of the SER and that MF may play a role in the movement of SER-vesicles to those areas of the cytoplasm where new RF are being formed.

Animals↗
PubMed1975

Ultrastructural localisation of calcium in peripheral nerves of the rat.

An ultrastructural method which is specific for calcium was applied in a study of calcium distribution in the axoplasm of myelinated nerve fibres of rat sciatic nerves. Electron-dense deposits of calcium oxalate were seen in smooth-membraned vesicles within the axoplasm, and between the two external membranes of axoplasmic mitochondria. The significance of calcium localisation at these sites is discussed, with special reference to the role of calcium in fast axoplasmic transport.

Animals↗