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Biomedical subjects

D F Sharman

Publications and source records attributed to D F Sharman.

At least 37 records · Page 2Linked to original sources
PubMed1986

Release of endogenous 5-hydroxytryptamine from the intermediate lobe of the rat pituitary gland is inhibited by endogenous dopamine.

The release of endogenous 5-hydroxytryptamine (5-HT) from the in vitro incubated neurointermediate lobe (NIL) of the rat hypophysis was measured by HPLC with electrochemical detection. 5-HT release evoked by electrical stimulation of the pituitary stalk from the NIL, but not from the isolated neural lobe (NL) was enhanced in the presence of the dopamine receptor antagonist sulpiride (1 microM). The opiate receptor antagonist naloxone (1 microM) had no effect on the evoked release of 5-HT from the NIL or NL. In conclusion, the release of endogenous 5-HT from the intermediate lobe is under inhibitory control of endogenous dopamine.

Animals↗
PubMed1986

A semi-automated fluorimetric method for measuring acetylcholinesterase activity in small volumes of cerebrospinal fluid and tissue extracts using acetylcholine as substrate.

A fluorimetric method for the assay of acetylcholinesterase (AChE; EC 3.1.1.7) in tissue extracts and cerebrospinal fluid, using acetylcholine as the substrate, is described. The method is based on the measurement of hydrogen peroxide, formed by the oxidation of choline resulting from the action of AChE on acetylcholine, by means of horseradish peroxidase and 4-hydroxy-3-methoxyphenylacetic acid (HVA) to yield a fluorescent derivative. Choline, if present in any sample to be analysed, is first removed by a modification of the peroxidase reaction during preincubation.

Acetylcholine↗
PubMed1986

Monoamines in tubero-hypophyseal structures of farm animals.

Dopamine (DA) and 5-hydroxytryptamine (5-HT) were measured in several regions of the pituitary gland of Jersey steers, Soay ewes and two breeds of pigs. The glands were collected from animals which had not been stressed and the amine concentrations were comparable to those found previously in the pituitary glands of laboratory animals. Metabolites of both amines were present in the infundibulum, the pituitary stalk, the combined neural and intermediate lobe and the anterior lobe of all glands analysed indicating that the amines are being utilized in these structures under "near physiological" conditions.

Animals↗
PubMed1986

Dehydration increases the electrically evoked dopamine release from the neural and intermediate lobes of the rat hypophysis.

The effect of dehydration on dopamine (DA) release from the neural and intermediate lobes of the rat pituitary gland after electrical stimulation of the pituitary stalk was studied in vitro. The amount of DA released from pituitary lobes of dehydrated rats (no water for 72 h), in which the hormone secretion from the hypophysis, especially the neural lobe, is known to be greatly enhanced, was significantly higher when compared with that from control tissues. In control and dehydrated rats the evoked DA release from the intermediate lobe was higher than that from the neural lobe. After dehydration, the stimulus-evoked DA release from the neural lobe increased by more than 200%, whereas that from the intermediate lobe increased by only 60%, indicating a preferential activation of the DA system of the neural lobe. There was a decrease in DA released per pulse from the combined neuro-intermediate lobe of control rats with increasing number of stimulation pulses. In contrast, DA release per pulse from the neuro-intermediate lobe of dehydrated rats showed a tendency to increase with increasing number of pulses. As the availability of newly synthesized DA is believed to be the limiting factor for transmitter release, the present observations suggested a higher in vitro DA synthesis rate in the tissues from dehydrated rats. This agrees with in vivo results of Alper and his colleagues who found an increased accumulation of L-3,4-dihydroxyphenylalanine (DOPA) in neuro-intermediate lobes of dehydrated rats after inhibition of DOPA-decarboxylase.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

Cerebrospinal fluid levels of acetylcholinesterase, monoamines and oxytocin during labour, parturition, vaginocervical stimulation, lamb separation and suckling in sheep.

Acetylcholinesterase (AChE) activity, and concentrations of monoamines, monoamine metabolites and oxytocin (OT) were measured in the cerebrospinal fluid (CSF) of sheep during late pregnancy, labour, parturition, vaginocervical stimulation, lamb separation and suckling. Concentrations of AChE, 4-hydroxy-3 methoxyphenylethan-1,2-diol (MHPG) and OT were significantly elevated during labour and parturition. OT levels were also significantly raised in cycling ewes given vaginocervical stimulation. Separation of the ewes from their lambs (0.5-2 h) caused significant increases in AChE and MHPG, but not in OT. During suckling, following reunion of the ewes and lambs, concentrations of AChE and OT were significantly raised. The dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly lower in CSF during late pregnancy than during parturition and post-partum. Intravenous injections of OT which produced high circulating levels of this hormone in plasma produced significant, but very small, increases in concentrations of OT in the CSF. Our results show that in the sheep, labour, parturition, suckling and vaginocervical stimulation provoke a release of OT in the brain similar to that in the peripheral circulation. Changes in CSF levels of AChE and MHPG during labour, parturition and lamb separation, but not during vaginocervical stimulation, may be related to stress or hypertension.

Acetylcholinesterase↗
PubMed1985

Pituitary 5-hydroxytryptamine nerves--a possible link with pituitary hormone secretion.

A short review of the present knowledge on the innervation of the pituitary gland by 5-hydroxytryptamine (5-HT) containing nerves is given. This is followed by results of recent experiments in which the concentrations of 5-HT in different lobes of the rat hypophysis were measured under conditions in which pituitary hormone secretion was increased. A prolonged increase in hormone secretion induced by dehydration and increased sodium chloride intake resulted in a decrease in the 5-HT concentrations in the anterior lobe (AL). The 5-HT content of the neural (NL) and the intermediate lobe (IL) of these rats was hardly changed whereas that of DA was about doubled. Acute stimulation of pituitary hormone secretion by exsanguination under ether anaesthesia also caused a fall in the 5-HT content of the AL. In contrast, in the NL and in the IL of these rats, the 5-HT concentrations were significantly increased. This indicates that the 5-HT system in the AL reacts differently from those in the NL and IL. Pituitary dopamine (DA) contents were not affected by ether and exsanguination. Thus, the pituitary DA and the pituitary 5-HT neuronal systems are activated independently in different endocrine states. The concentrations of 5-HT were also measured in 10 groups of normal male or female rats in the course of 2 years and compared with those of DA. The concentrations of 5-HT were lowest in the AL with little variation between the different groups. In the rest of the tubero-hypophyseal system the concentrations of 5-HT were at least 3, and up to 10 times, higher than in the AL, with larger inter group variations. The DA concentrations in the AL were only 10-20% of those of 5-HT; in the other regions they were equal to or higher than those of 5-HT.

Acute Disease↗
PubMed1985

Release of endogenous 5-hydroxytryptamine from the neural and the intermediate lobe of the rat pituitary gland evoked by electrical stimulation of the pituitary stalk.

A calcium-dependent release of 5-hydroxytryptamine from the neural and intermediate lobe of the rat pituitary gland has been demonstrated following electrical stimulation of the pituitary stalk with stimulation parameters thought to evoke propagated action potentials. The 5-hydroxytryptamine release from the intermediate lobe was double that from the neural lobe. The mass of the intermediate lobe of the rat is about 80% of that of the neural lobe [Holzbauer, Racké, Mann, Cooper, Cohen, Krause and Sharman (1984) J. Neural Transm. 59, 91-104]. The relatively high overflow of 5-hydroxytryptamine from the intermediate lobe agrees with immunohistochemical studies in which a larger number of 5-hydroxytryptamine fibres were seen in the intermediate lobe than in the neural lobe. The present results have demonstrated that the rat hypophysis contains neuronal 5-hydroxytryptamine. They also suggest that this amine may act as a neurotransmitter substance in the neural and intermediate lobe.

Animals↗
PubMed1985

An analysis of some behavioural effects of the vibration and noise components of transport in pigs.

The reactions of pigs to the vibration and noise components of transport were examined with the use of an apparatus which simulated these factors. The pigs were trained to switch off the apparatus by pressing a switch panel with their snouts. It was found that vibration was aversive but that noise was not. The pigs switched off the apparatus more frequently when the vibration was fast and when they had been fed a large meal before the test. Although the sedative tranquillizing drug azaperone decreased the number of times the apparatus was switched off, the effect appeared to be non-specific because azaperone also reduced the number of responses that pigs would make in order to receive food.

Animals↗
PubMed1984

Immunoreactive substance P in the tubero-hypophyseal system of the rat: selective decrease in the neural lobe after dehydration and sodium loading.

In the tubero-hypophyseal system of the rat the approximate concentrations of immunoreactive substance P (I-SP), expressed as fmol/mg tissue, were 100 in the medial basal hypothalamus (MBH), 20 in the anterior lobe (AL), 20 in the neural lobe (NL) and 4 in the intermediate lobe of the hypophysis. These values were not altered by treatment with capsaicin on day 2 after birth. In rats in which the secretion of neurohormones from the NL was increased by dehydration followed by sodium loading there was a fall by 70% in the I-SP concentration of the NL; no change occurred in the AL or the MBH.

Animals↗
PubMed1984

Regional differences in the effect of pargyline on dopamine concentrations in the rat hypophysis.

Dopamine concentrations were estimated in different regions of the infundibular-pituitary system of the rat. The highest values were found in the pituitary stalk where they are comparable to the concentrations in the striatum, and higher than in the median eminence. In the anterior lobe the dopamine (DA) concentrations of the upper pole (10% of the lobe tissue) were 2-5 times higher than in the rest of the lobe. Anterior lobe DA was significantly higher in rats about 6 months old than in rats about 3 months old. After inhibition of MAO, the DA concentrations in the isolated neural lobe (NL) were more than doubled. In contrast there was no increase in the DA concentrations of the intermediate lobe, an observation which is in agreement with our previous finding that DA synthesis in the intermediate lobe after electrical stimulation of the pituitary stalk is much slower than in the neural lobe. Pargyline treatment caused an increase in the DA concentrations in the anterior lobe by about 150%. This rise (together with a DA increase in the stalk-infundibulum) may be related to the decrease in circulating prolactin which occurs in pargyline treated rats.

Aging↗
PubMed1983

Changes associated with early weaning in the activity of tyrosine hydroxylase in the caudate nucleus of the piglet.

1. Early weaning in piglets is associated with changes in dopamine metabolism in the caudate nucleus. In particular, a decrease in the amount of the enzyme tyrosine hydroxylase was observed. 2. An analysis of the kinetic properties of tyrosine hydroxylase from the caudate nucleus of early-weaned piglets shows that there is a relative increase in the activity of the enzyme which may indicate a mechanism compensating for the decreased amount of enzyme. 3. The increase in activity is mediated through a decrease in the Km for tetrahydrobiopterin and is reversed, in vitro, when the tissue is homogenized at pH values greater than 8.0.

Animals↗
PubMed1983

The metabolism of dopamine in the blood of ruminant animals: an enzyme system to metabolize dopamine released from the mast cells in these species?

Following the i.v. administration of 3,4-dihydroxyphenylethylamine (dopamine) to sheep, 3,4-dihydroxyphenylethanol and 3,4-dihydroxyphenylacetic acid rapidly appeared in the blood. 3,4-Dihydroxyphenylethanol can be formed from dopamine by blood plasma of ruminants in vitro. It is suggested that this plasma enzyme system might serve to inactive dopamine released from mast cells in ruminant species.

3-Methoxy-4-hydroxyphenylethanol↗
PubMed1983

Dopamine in the blood platelets of the sheep.

The concentrations of dopamine and noradrenaline were measured in sheep blood platelets using high performance liquid chromatography and electrochemical detection. The concentration of dopamine was estimated to be 0.0012 microgram/10(9) platelets and that of noradrenaline, 0.0045 microgram/10(9) platelets.

Animals↗
PubMed1983

An investigation into some cerebral mechanisms involved in schedule-induced drinking in the pig.

When pigs were fed small amounts at regular short intervals (5-10 min), drinking followed each ingestion. This resulted in a greatly increased total water intake (schedule-induced polydipsia: s.i.p.). Injection of angiotensin II into the lateral cerebral ventricle of water-replete pigs on normal feeding also produced a significant increase in water intake. Prior administration of the angiotensin II antagonist, saralasin, attenuated the dipsogenic effect of angiotensin II, but did not modify s.i.p. The tranquilizing drug, azaperone, had no effect on normal water intake and did not modify the response to angiotensin II. However, azaperone reduced the water intake of animals on scheduled feeding. From this, it was concluded that the increased drinking due to scheduled feeding did not involve the renin-angiotensin system but it is tentatively suggested that it may involve central dopaminergic neuronal systems.

Angiotensin II↗
PubMed1983

A comparison of the release of endogenous dopamine from the neural and the intermediate lobe of the rat hypophysis after electrical stimulation of the stalk.

Dopamine (DA) was released from the isolated neural lobe of the pituitary gland by electrical stimulation of the pituitary stalk. This observation completes the evidence for DA to be classified as a neurotransmitter substance in the neural lobe in the rat hypophysis. From the experiments on the isolated neural lobe and simultaneous experiments on the combined neuro-intermediate lobe it could be calculated that the DA release from the intermediate lobe was about three times larger than that from the neural lobe. Electrical stimulation of the pituitary stalk in the presence of pargyline and TEA led to an increase in DA synthesis in the neural lobe. This effect did not occur in the intermediate lobe.

Animals↗