Autonomic control of protein production by the parotid gland of the sheep.

The role of adrenoceptors in the control of parotid salivary function has been investigated in anaesthetized sheep. The enhancement of parotid protein output that occurs when the parasympathetic and sympathetic innervations to the gland are stimulated simultaneously in bursts at a low frequency (20 Hz for 1 s at 10-s intervals) was effectively abolished by pretreatment with propranolol (> or = 1.0 mg kg(-1), i.v., P < 0.001), without a comparable reduction in the flow of saliva or in the output of sodium or potassium. Secretion of protein was similarly augmented by simultaneous stimulation of the sympathetic innervation and an intracarotid infusion of acetylcholine (0.4-0.6 microg min(-1) g gland(-1)). This effect was also abolished by pretreatment with propranolol. Pretreatment with phentolamine (>1.0 mg kg(-1), i.v.) had no effect on the output of protein that occurred during combined stimulation of the parasympathetic and sympathetic innervations but increased the flow of saliva and the output of electrolytes. Stimulation of the parasympathetic innervation to the parotid gland caused a substantial fall in vascular resistance, which was reduced by the administration of atropine (0.5 mg kg(-1)). Stimulation of the sympathetic innervation caused a substantial rise in parotid vascular resistance in atropinized sheep. This effect was greater during continuous stimulation than during intermittent stimulation and enhanced by pretreatment with propranolol. It was virtually eliminated by pretreatment with phentolamine. It is concluded that the enhancement of protein output from the ovine parotid gland, that occurs during combined stimulation of the parasympathetic and sympathetic innervations at relatively low frequencies, depends upon interaction between cholinergic muscarinic and beta-adrenergic receptors. The vasoconstriction that occurs during sympathetic stimulation alone can be accounted for by activation of alpha-adrenoceptors.

The effect of parasympathetic postganglionic denervation on parotid salivary protein secretion in anaesthetized sheep.

Effects of unilateral parasympathetic denervation of ovine parotid glands were examined in anaesthetized sheep 21-28 days after nerve section. Parasympathetic denervation reduced the mass of the ipsilateral gland while increasing that of the contralateral gland to the extent that total gland mass was greater than in sheep with normally innervated glands. The spontaneous secretion (8.8 +/- 1.1 microl min(-1) g gland(-1)) was significantly less from denervated than from innervated glands of normal control animals (26.0 +/- 2.7 microl min(-1) g gland(-1); P< 0.01) and contained more protein. Rates of flow, and the outputs of sodium and potassium, in response to sympathetic stimulation, were similar from normally innervated and chronically denervated glands, when allowance was made for the discrepancy in weights, whereas the output of protein was significantly enhanced following parasympathetic denervation (innervated--31.4 +/- 7.3 microg g gland(-1), denervated--83.4 +/- 26.6 microg g gland(-1); P< 0.05). Intra-arterial infusions of acetylcholine (130 pmol min(-1) kg(-1)) elicited a flow of parotid saliva, the protein content of which was significantly enhanced by prior parasympathetic denervation. Intra-arterial infusions of vasoactive intestinal peptide (VIP; 2.5 pmol min(-1) kg(-1)) produced a small but statistically significant (P< 0.05) increase in the flow of parotid saliva from the contralateral, innervated but not from denervated glands. It also caused a small increase in protein output, which was significantly enhanced by prior denervation. VIP had no synergistic effect on the parotid responses to acetylcholine. The results show that the parasympathetic innervation to the parotid gland of the sheep exerts important trophic effects on the gland. Interaction of adrenergic and cholinergic receptors makes an important contribution to stimulation of the secretion of protein and prior denervation potentiates the protein responses to both acetylcholine and VIP.

Synergism in the autonomic regulation of parotid secretion of protein in sheep.

1. Stimulation of the cervical sympathetic nerve continuously at 2 Hz, or in bursts of 1 s at 20 Hz every 10 s, for 5 min doubled the resting flow of parotid secretion in anaesthetized sheep and increased its concentration of protein. It also caused a significant increase in the concentration of potassium and decreased that of sodium: these latter effects were linearly inversely related. 2. Stimulation of the parotid nerves (the parasympathetic innervation) continuously at 2 Hz increased the flow of parotid secretion over 15-fold which was significantly more than that which occurred in response to stimulation in bursts at 20 Hz. However, the latter pattern of stimulation significantly increased the concentration of protein in the saliva, which was not altered by stimulation at 2 Hz continuously. 3. Simultaneous stimulation of both the parotid and sympathetic nerves at 20 Hz in bursts substantially increased the output of protein from the gland, above that recorded in response to stimulation of either alone, without potentiating either the volume of secretion produced or the outputs of sodium or potassium. 4. The output of protein was also potentiated when both nerves were stimulated simultaneously at 2 Hz continuously but this pattern of stimulation elicited the secretion of a significantly smaller amount of protein. 5. All parotid responses to stimulation of the parotid nerves, either continuously at 2 Hz or in bursts at 20 Hz, were abolished by atropine (greater than or equal to 0.5 mg kg-1 I.V.), as was potentiation of protein secretion during combined stimulation with the sympathetic innervation. 6. Stimulation of the parotid nerves in bursts at a higher frequency (60 Hz for 1 s at 20 s intervals) elicited a sparse flow of parotid saliva in atropinized animals without significant increase in protein output, with or without simultaneous stimulation of the sympathetic innervation. 7. The results of these experiments show that secretion of protein by the parotid gland, in response to stimulation of the parasympathetic innervation, depends on the pattern of stimulation and is potentiated by concomitant stimulation of the sympathetic innervation in anaesthetized sheep.

A minor globin gene of the bivalve mollusc Anadara trapezia.

A minor haemoglobin gene was isolated from an Anadara trapezia genomic library using a synthetic oligonucleotide probe based on the identical amino acid sequence of the F-helical region of all the major Anadara globins previously sequenced. The amino acid sequence inferred from the coding region of the gene indicated that it is different from that of the three major chains alpha, beta and gamma, but most like the beta-chain. This beta-variant sequence shows 100% homology in the conserved F-helix region. The minor gene was found to contain two long intervening sequences, 1214 bp and 1435 bp, longer than those present in the genes for vertebrate globins or leghaemoglobins but shorter than those in myoglobin genes.

Atropine-resistant secretory responses of the ovine parotid gland to reflex and direct parasympathetic stimulation.

A study was made of mechanisms involved in the parasympathetic control, especially of protein concentration in, and also flow, of ovine parotid secretion. The effects of distension of the caudal thoracic oesophagus were characterized in four anaesthetized sheep each with a unilateral chronic superior cervical sympathetic ganglionectomy. Oesophageal distension produced increases in both the flow and protein concentration of saliva from the control glands similar to that from the sympathectomized glands indicating the response was mediated by the parasympathetic innervation. Atropine, in doses which completely abolished increases in flow and protein concentration produced by bethanechol infusion, reduced, but did not abolish, the responses to oesophageal distension providing evidence of non-cholinergic transmission. Electrical stimulation of the parotid (parasympathetic, postganglionic) nerve during atropinization produced ca. 70% increases in flow and ca. 100% increases in protein concentration of parotid saliva thus giving further evidence of such a mechanism. Intracarotid infusion of vasoactive intestinal polypeptide (VIP) evoked responses with similarities to those observed with oesophageal distension and nerve stimulation during atropinization. This observation adds to other evidence indicating that VIP acts as a parasympathetic neurotransmitter involved in the control of salivary secretion.

Effects of the vagus nerves on gastric motility and release of vasoactive intestinal polypeptide in the anaesthetized lamb.

1. Effects of the vagus nerves on the activity of the reticulo-omasal orifice (ROO) and the abomasum and the concentration of vasoactive intestinal polypeptide (VIP) in gastric and intestinal venous effluent were studied in anaesthetized lambs. 2. Both excitatory and inhibitory effects of the vagus on the ROO and abomasum were demonstrated. Excitation of activity of the ROO was dominant with stimulation at lower frequencies (less than or equal to 20 Hz) whereas higher frequencies (50-70 Hz) caused inhibition. 3. Inhibition but not stimulation of the ROO and abomasum were obtained with vagal stimulation after administration of atropine (200-500 micrograms kg-1 I.V.). 4. The concentration of VIP in gastric venous effluent blood rose by 41 +/- 10 pmol l-1 (n = 13) within 90 s of the start of stimulation (10 Hz, 5 ms pulse duration, 10 V for 180 s) of a vagus nerve and fell within 60 s of its cessation to or near basal levels. The effects of vagal stimulation in changing the concentration of VIP were not altered by administration of atropine. 5. The concentration of VIP in the intestinal venous effluent increased during stimulation (10 Hz, 5 ms pulse duration, 10 V, for 180 s) of a vagus nerve by 15 +/- 5 pmol l-1 (n = 11) and remained elevated for more than 10 min after the stimulus had ceased. 6. The changes in gastric motility and in concentration of VIP in gastric and intestinal venous blood with stimulation of the vagus nerves have been discussed in relation to similar alterations which occur in lambs during sucking of milk.

Gastric electromyographic activity in the milk-fed lamb.

1. Electromyographic (EMG) activity of the reticulum, reticulo-omasal orifice (ROO) and abomasum was recorded from conscious lambs. 2. In fasted lambs diphasic reticular EMG bursts occurred at intervals of 60 +/- 13 s. In association with the second phase of the reticular EMG burst there was consistently a period of inactivity of the EMG of the ROO of 2.4-11.0 s (5.5 +/- 2.0 s, mean +/- S.D.). This period of quiescence ended with the onset of a burst of EMG activity of the ROO of 4.1 +/- 0.8 s termed here a long burst of activity. Preceding the following reticular EMG burst there were further long bursts of EMG activity of the ROO at intervals of 11.1 +/- 1.3 s or intermixing or replacement of long burst activity with short bursts which were of duration 1.1 +/- 0.3 s and which occurred at intervals of 2.4 +/- 0.5 s. 3. When the lambs were shown milk and at times when they could be expected to anticipate milk being provided, a period of inactivity of the EMG of the ROO developed for up to 60 s. In association with this there was commonly an increase in the frequency of reticular EMG bursts which at times became monophasic. 4. With the start of sucking there was quiescence of the EMG of the ROO which persisted throughout periods of sucking for up to 90 s. Simultaneously with the disappearance of activity of the ROO there was a monophasic burst of the reticular EMG, which was followed by either quiescence or disorganized low voltage activity. Inactivity of the EMG of the ROO still developed when lambs sucked milk after administration (I.V.) of atropine, phentolamine or propranolol, but not after hexamethonium. 5. In lambs observed over a period 30-60 min after feeding the diphasic reticular bursts occurred every 85 +/- 24 s and the duration of the period of inactivity of the EMG of the ROO associated with each reticular burst (3.7 +/- 1.2 s) was significantly less (P less than 0.001) than in fasted lambs. Short bursts of EMG activity of the ROO occurred more frequently than in fasted lambs. 6. In fasted lambs bursts of EMG activity of the body of the abomasum occurred at frequencies of 6-12 min-1 and those of the antrum and pylorus at ca. 6 min-1 but episodes of such activity were intermittent.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of vasoactive intestinal polypeptide on gastric motility in the lamb.

1. Intra-arterial infusions of vasoactive intestinal polypeptide (VIP) were made in anaesthetized lambs in which activity of the reticulo-omasal orifice (ROO) was recorded manometrically and in conscious lambs in which activity of the reticulum, ROO and abomasum were recorded by electromyographic (EMG) techniques. 2. Spontaneous rhythmic opening and closing movements of the ROO occurred in anaesthetized lambs at 3-5 min-1. Infusions of VIP into the left gastric artery at rates of 0.5-3.0 nmol min-1 produced changes in activity of the ROO. Within 120 s of commencement of the infusions there was an increase in frequency and magnitude of the movements of the ROO for up to 120 s. This was followed with infusion of VIP at the lower levels (0.5-1.0 nmol min-1), by a marked reduction and sometimes complete loss of the rhythmic movements. There was always complete cessation of activity of the ROO with infusion of VIP at 1.5-3.0 nmol min-1. 3. In conscious lambs the frequency of the diphasic reticular EMG bursts which recur at intervals of ca. 1 min was not affected by infusions of VIP at 3.0 nmol min-1 for 10 min. 4. Between each diphasic reticular EMG burst in the conscious lamb there was normally phasic activity of the ROO consisting of EMG bursts of long (ca. 4 s) and short (ca. 1 s) duration. Within 90 s of commencement of infusion of VIP at 3.0 nmol min-1 short-burst EMG activity disappeared with the remaining long bursts being of greater duration (5.4 +/- 1.2 s) than before infusion. After a series of four to fifteen such more prolonged long bursts there was quiescence of the EMG of the ROO. After infusion of VIP EMG activity recommenced first as a series of eight to fourteen long bursts which was followed by the reappearance also of short-burst activity. Infusions of VIP at 8-10 nmol min-1 produced a more prompt cessation of EMG activity of the ROO. Of other peptides which were infused only PHI (a peptide with N-terminal histidine and C-terminal isoleucine amide) produced cessation of the EMG activity of the ROO. However, on a molar basis VIP was 2-3 times more potent than PHI in causing cessation of activity of the ROO. 5. Infusion of VIP at 3.0 nmol min-1 produced a cessation or diminution of EMG activity of the body, antrum and pylorus of the abomasum.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunochemical characterisation of somatostatin in ruminants.

Following development and validation of a radioimmunoassay for somatostatin, the immunoreactivity of this peptide in the plasma of ruminants was measured and the levels in sheep were 9-31 pM (mean 18 +/- 7 pM, n = 48), in lambs 10-54 pM (mean 25 +/- 10 pM, n = 18) and in calves 5-35 pM (mean 12 +/- 6 pM, n = 22). Somatostatin-like immunoreactivity was present in sheep in high concentrations in the antrum (2342 +/- 280 pmol/g wet weight), duodenum (446 +/- 73 pmol/g) and pancreas (832 +/- 208 pmol/g). Lower concentrations (6-150 pmol/g) were found in other regions of the gastrointestinal tract. Molecular sieve chromatography on Bio-Gel P-10 showed that while most of the somatostatin in the antrum was somatostatin-14, in the duodenum about 30% of the total immunoreactivity was somatostatin-28.

Effects of lys-beta-urogastrone in vivo.

Lys-beta-urogastrone, an analogue of human beta-urogastrone with an additional N-terminal lysine, was shown to have similar effects in mice and sheep to mouse epidermal growth factor (mEGF). Lys-beta-urogastrone in doses of 0.18-3.24 micrograms g-1 body weight caused both precocious separation of eyelids and eruption of incisors in neonatal mice. In 17 sheep, intravenous infusion of the urogastrone analogue over c. 24 h led, towards the end of infusion, to erythema of the muzzle, caused reductions in voluntary food intake (with doses greater than or equal to 50 micrograms kg-1) and generally easier manual harvesting of the fleece (with infusions greater than or equal to 81 micrograms kg-1), with spontaneous shedding of the fleece (c. 14 days after infusions of greater than or equal to 116 micrograms kg-1). In five sheep infusions of 25, 38, 50, 83 and 118 micrograms kg-1 fleece-free body weight, plasma concentrations of lys-beta-urogastrone were near maximal 20 h after the infusions started and were, respectively, 1.1, 1.7, 5.5, 18 and 79 micrograms l-1 plasma. Plasma concentrations of gastrin, somatostatin and pancreatic polypeptide were determined in these five sheep. Plasma gastrin rose sixfold by the end of infusions of 25 micrograms kg-1 of the urogastrone analogue, and tenfold with the higher doses of infusion. Although plasma somatostatin concentrations were variable, a consistent trend was observed; lower levels were apparent during the lys-beta-urogastrone infusions. There was no discernible trend in pancreatic polypeptide concentrations.

Gastric and intestinal release of vasoactive intestinal polypeptide in the milk-fed lamb.

Vasoactive intestinal polypeptide (VIP) has been proposed as the neurotransmitter of the atropine-resistant relaxation of gastric structures in the lamb. To examine this proposal VIP concentrations in plasma from arterial, gastric venous and intestinal venous blood were measured in healthy conscious lambs before, during and after teasing with, and sucking of milk. Basal arterial plasma VIP concentrations were undetectable (less than 3 pmol/l) and remained so during and after feeding. Before feeding VIP was detected in only 2 of 12 gastric venous plasma samples (5 and 13 pmol/l). During teasing with food there were increments in VIP of 19 +/- 4 pmol/l and during feeding of 27 +/- 5 pmol/l. VIP concentration in gastric venous plasma rapidly returned to fasting levels after cessation of sucking. In contrast VIP in the intestinal venous plasma did not rise during teasing or upon commencement of sucking but a peak increment of 34 +/- 6 pmol/l occurred at 5 min after cessation of feeding. The results are consistent with the hypotheses that VIP is released in anticipation of and during sucking from inhibitory neurones involved in relaxation of gastric structures and that intestinal release of VIP is a consequence of entry of digesta into the small intestine.

Plasma gastrin in the pig from birth to weaning.

Mean (+/- SEM) plasma gastrin concentration was measured as 84.4 +/- 7.0 pmol litre-1 by radioimmunoassay in 35 newly born pigs within one hour of birth but, two-and-a-half hours later, after sucking, it had decreased to 34.9 +/- 3.6 pmol litre-1. Significant increases (P less than 0.01) in the concentration of plasma gastrin occurred in the three weeks after birth to 142.5 +/- 13.2 pmol litre-1 at one week, 174.8 +/- 15.7 pmol litre-1 at two weeks and 91.4 +/- 9.6 pmol litre-1 at three weeks after birth. On weaning, at four weeks old, plasma gastrin concentration was 26.0 +/- 1.7 pmol litre-1 and at five and six weeks old it was 56.7 +/- 4.4 and 54.7 +/- 3.9 pmol litre-1, respectively.

Motilin and migrating myoelectric complexes in the pig and the dog.

Associations between migrating myoelectric complexes (m.m.c.s) and peak plasma motilin concentrations were confirmed in the dog fasted 18 h and shown not to be present in pigs fasted 3-4 h. Infusions of both natural porcine and synthetic 13-Nle-motilin failed to induce m.m.c.s in the pig. It was confirmed that motilin infusions stimulated the premature appearance of m.m.c.s in the dog whether motilin remained within, or exceeded, its normal plasma values. Immunoneutralization by intravenous administration of rabbit antimotilin serum was without effect on naturally occurring m.m.c.s in the dog and the pig. In the dog, antimotilin serum blocked production of m.m.c.s by exogenous motilin for 7-10 d post-immunoneutralization. It is suggested that there are both: (i) species differences in associations of m.m.c.s and plasma motilin concentration, and (ii) an independence of m.m.c.s from plasma motilin even in the dog in which normally exogenous motilin can produce m.m.c.s.

Immunoreactive gastrin concentrations in gastrointestinal tissues of sheep.

Radioimmunoassay of gastrin in gastrointestinal tissues of lambs and adult sheep showed highest concentrations (796 to 11,156 pmol g-1 mucosa) in the antral region of the abomasum. The next highest concentrations of gastrin were in the proximal duodenal mucosa (16 to 518 pmol g-1). Gastrin was undetectable or present in lower concentrations in caudal regions of the duodenum (less than 11 X 5 pmol g-1), the pancreas and in the body of the stomach. It is concluded that the distribution of gastrin secreting cells in sheep is similar to that in other animals.

Manometric and electromyographic observations of the oesophagus of sheep in eructation, regurgitation and swallowing.

Manometric and electromyographic recordings during eructation, swallowing and the regurgitation of rumination in sheep revealed variable oesophageal activity during eructation in contrast to the uniform pattern of oesophageal activity in swallowing and regurgitation. In eructation the passive increase in pressure of about 7-15 mmHg--the filling phase--associated with entry of gas into the oesophagus was commonly (in 96.6% of thirty eructations) terminated by contractions in the caudal thoracic oesophagus (c.t.o.). Eructation contractions were present in 73.3% of thirty eructations in a site 130 mm cranial to the c.t.o. and in 36.6% of thirty eructations in a site 260 mm cranial to the c.t.o. These contractions moved cranially at about 420 mm.s-1. In contrast during regurgitation the contractions of the oesophagus which moved cranially at about the same rate (410 mm X s-1) were characteristically more intense (47-64 mmHg) than eructation contractions (10-36 mmHg). Also in contrast to those in eructation, regurgitation contractions were invariably of each site of the oesophagus from which recordings were made. Secondary contractions of the caudal cervical and thoracic oesophagus which sometimes followed eructation were interpreted as serving as clearing contractions returning residual gas in the oesophagus to the stomach. These swept over the oesophagus at about 200 mm X s-1 and occurred without associated swallows. The variability of reactions of the oesophagus in eructation and differences in reactions of its different regions are discussed as arising from different degrees of sensitivity to, and stimulation by, gaseous distension of the oesophagus and stomach.

beta-Adrenergic effects on composition of parotid salivary secretion of sheep on feeding.

Observations were made in sheep, before and after fresh food was given during teasing with food and after rumination, on the flow of parotid saliva and its protein Mg2+, K+, Na+ and Cl- concentrations. The animals studied had either a cannulated or fistulated parotid salivary duct. Parotid salivary flow, protein, Mg2+, K+ and Cl- increased markedly following feeding. The increases in protein and Mg2+, but not in flow, were largely blocked by the i.v. administration of propranolol (1 mg . kg-1). Whereas the actual ingestion of food was associated with large increases in protein (up to 42.5 times, to as high as 1760 micrograms . ml-1 of saliva), teasing with food caused relatively minor increases in parotid saliva. There were slight, if any, changes in protein concentration during the increased parotid salivary flows of rumination, whether chewing was on the same side or contralateral to the cannulated parotid salivary duct. It is concluded that a beta-adrenergic mechanism previously demonstrated in acute experiments contributes to increases in the secretion of protein of the parotid saliva when sheep eat. There was a close correlation between the concentrations of protein and of Mg2+ but not of the other electrolytes studied.