Susan Tomlin

INCREASED β-ENDORPHIN BUT NOT MET-ENKEPHALIN LEVELS IN HUMAN CEREBROSPINAL FLUID AFTER ACUPUNCTURE FOR RECURRENT PAIN

Low-frequency electroacupuncture effectively alleviated recurrent pain in 10 patients. Basal levels of beta-endorphin and met-enkephalin in the lumbar cerebrospinal fluid (CSF) of these patients were not different from those in pain-free control subjects. After electroacupuncture in the patients with pain CSF beta-endorphin levels rose significantly in all subjects, but met-enkephalin levels were unchanged. These results suggest that the analgesia observed after electroacupuncture in patients with recurrent pain may be mediated by the release into the CSF of the endogenous opiate, beta-endorphin.

CORTICOTROPHIN RELEASING FACTOR: RESPONSES IN NORMAL SUBJECTS AND PATIENTS WITH DISORDERS OF THE HYPOTHALAMUS AND PITUITARY

Synthetic CRF‐41 has been given to 43 patients with hypothalamic, pituitary or adrenal diseases and contrasted with the responses in 20 normal subjects. In the normal subjects the mean increment in serum cortisol (± SE) was 276 ± 38 nmol/l; the increments showed a significant negative correlation with the basal serum cortisol levels (r= ‐0·56; P<0·02). The mean peak serum cortisol was 662 ± 34 nmol/1 and the mean peak corticosterone was 28·6 ± 3·8 nmol/1. There was a significant positive correlation between the peak serum corticosterone and cortisol concentrations (r= 0·84; P<0·0001). Dexamethasone pretreatment abolished the rise in cortisol in response to CRF‐41. The peak serum cortisol following CRF‐41 was not significantly different between the normal subjects and those patients with pituitary disease who had normal cortisol responses to insulin‐induced hypoglycaemia. However, in individual patients the peak cortisol levels induced by hypoglycaemia were greater than, but significantly correlated with, those induced by 100 μg of CRF‐41. Seven patients were ACTH deficient in response to hypoglycaemia, and of these six responded normally to CRF‐41. Only one of these patients had a lesion clearly originating in the hypothalamus; four had pituitary tumours with suprasellar extensions and the remaining patient had idiopathic GH and ACTH deficiency. Our data suggest that these patients have a functional defect of ACTH secretion due to the failure of CRF to reach the corticotroph. Of the four patients with pituitary‐dependent Cushings disease who were on no treatment at the time of testing, three showed an exaggerated and one a normal response to CRF‐41. These normal or enhanced responses of hypercortisolaemic patients with Cushings syndrome contrast with the complete inhibition of the responses to CRF‐41 in normal subjects given dexamethasone. In the treated patients with Cushings syndrome

Alpha-Adrenergic Stimulation of Corticotropin Secretion by a Specific Central Mechanism in Man

In a double-blind study in normal subjects, methoxamine, a highly selective agonist at alpha-1-adrenoceptors, significantly increased circulating ACTH and cortisol. The stimulant effect of methoxamine on cortisol secretion was dose dependent in the range 3.5-7 micrograms/kg/min, was abolished by concomitant administration of the strong alpha-1-adrenergic (and weak H1) antagonist thymoxamine but unaffected by the antihistamine, chlorpheniramine. In order to test whether the action of methoxamine on ACTH secretion was exerted centrally or peripherally, the effects of norepinephrine (NE), an alpha-1-agonist that does not cross the blood-brain barrier, were studied. Doses of NE (1-12 micrograms/min) that increased systolic blood pressure by amounts similar to the changes produced by methoxamine, did not result in any rise in plasma cortisol in normal subjects. The effect of methoxamine, which is more lipid soluble than NE, on plasma ACTH and cortisol, appears to be exerted on the CNS and not at the pituitary or via nonspecific peripheral mechanisms. In addition to its water solubility, NE differs from methoxamine in its beta-1-, beta-2- and alpha-2-agonist actions. However, prenalterol (2 mg) and salbutamol (250 micrograms), respectively beta-1- and beta-2-adrenergic agonist drugs, had no effect on the secretion of ACTH or cortisol and the alpha-2-antagonist yohimbine in an effective dose did not unmask a stimulant effect of intravenous NE on plasma cortisol. At high infusion rates, NE significantly inhibited cortisol secretion. Stimulation of central alpha-1-adrenergic mechanisms results in secretion of ACTH in man, presumably by increased release of a corticotropin-releasing factor.

Experience with selective venous sampling in diagnosis of ACTH-dependent Cushing's syndrome.

Twenty-three patients with adrenocorticotrophic hormone-(ACTH)-dependent Cushings syndrome were subjected to selective venous catheterisation and sampling for ACTH on a total of 26 occasions. Out of 10 patients with pituitary-dependent disease, nine had raised ACTH concentrations in one or both high internal jugular vein samples. Eight patients had 11 proved sites of ectopic hormone production: of these, six were correctly identified by the sampling technique, and in four of them this was the only accurate method of localisation. The results of one catheterisation were misleading, and on 10 occasions they were inconclusive; five patients remained undiagnosed by any method. Overall, 15 of the 26 catheterisations provided diagnostically valuable information. Selective venous catheterisation and sampling for ACTH is effective in confirming a pituitary source of the hormone and may be valuable in locating the source of ectopic ACTH production in some cases.

A STUDY OF THE RELATIONSHIP BETWEEN CIRCULATING β‐ENDORPHIN‐LIKE IMMUNOREACTIVITY AND POST PARTUM ‘BLUES’

Plasma β‐endorphin‐like immunoreactivity was studied in 43 pregnant women at 36 weeks gestation and in 23 of these at delivery and 24 h post‐partum; an attempt made to correlate changes with various social, psychological and obstetric factors, including the ‘post‐natal blues’. β‐endorphin levels were elevated at 36 weeks gestation and term, increased to very high levels during labour and fell rapidly within 1 h of delivery. A negative correlation was observed between the womans estimate of her pain in labour and the β‐endorphin levels post‐partum, suggesting an analgesic role for β‐endorphin in labour. A positive correlation was also observed between the levels of β‐endorphin at delivery and the womans attitude to her pregnancy at 36 weeks and a negative correlation between the ‘post‐natal blues score’ and the β‐endorphin level at 36 weeks. However, the ‘blues’ did not correlate either with the β‐endorphin level at delivery or 24 h post‐partum nor with its rate of fall in the first 24 h. Our general finding that there was no consistent social, psychological or obstetric factor which predisposes women to develop ‘post‐natal blues’ still supports the hypothesis that humoral factors, of which β‐endorphin may be one, rather than psychological factors are important in the genesis of this syndrome.

Endogenous opioid peptides in pregnancy.

Summary. Plasma levels of two endogenous opioid peptides, β‐endorphin and met‐enkephalin, as well as immunoreactive N‐terminal β‐lipotrophin (N‐LPH) were studied in normal pregnant women from 8 to 41 weeks gestation. A total of 116 samples were assayed for β‐endorphin‐like immunoreactivity (C‐LPH), 103 for N‐LPH and 75 for met‐enkephalin. Plasma β‐endorphin‐like immunoreactivity and N‐LPH levels rose progressively throughout gestation and reached a maximum at term. Plasma met‐enkephalin immunoreactivity did not significantly change throughout pregnancy. These results reflect an increasing and consistent adreno‐corticotrophin (ACTH)/β‐LPH and β‐endorphin secretion throughout pregnancy, while the unchanged met‐enkephalin levels are compatible with its known derivation from a separate precursor system.

CRF-41 Stimulates the Release of β-Lipotrophin and β-Endorphin in Normal Human Subjects

A prompt rise in circulating immunoreactive N- and C-terminal lipotrophin (LPH) accompanied the increase in ACTH when 100 µg CRF-41 was given to 6 normal male subjects. Chromatography of the basal and peak 15-min values showed that there was an equimolar increase in β-LPH and β-endorphin. to cause parallel release of ACTH, β-endorphin and β-LPH from the pro-opiocortin precursor.

Regional distribution of pro-opiomelanocortin-derived peptides in the human brain

The regional distribution of pro-opiocortin-derived peptides and methionine enkephalin was investigated in human brain post-mortem. Sequence-directed radioimmunoassays for beta-endorphin, gamma-lipotropin, adrenocorticotrophin, corticotrophin-like intermediate lobe peptide (ACTH18-39, CLIP) alpha-MSH and methionine enkephalin were used and 40 different human brain areas were assayed. The regional distribution of all the pro-opiomelanocortin-derived immunoreactivities were correlated with highest amounts of beta-endorphin, gamma-lipotropin and ACTH in the hypothalamus, amygdala, periventricular grey, substantia nigra and superior colliculus. The distribution of beta-endorphin, gamma-lipotropin and ACTH did not parallel the distribution of methionine-enkephalin immunoreactivity which was present in the globus pallidus, nucleus accumbens and substantia nigra. Gel exclusion chromatography (G-50) showed that pro-opiocortin-related peptides in the human hypothalamus and periventricular grey separated in positions consistent with the major immunoreactive forms being beta-endorphin, gamma-lipotropin, ACTH and CLIP.

Plasma levels and biochemical characterisation of circulating met-enkephalin in canine endotoxin shock

Endogenous opioid peptides have been implicated in the pathophysiology of shock (1-5). In anaesthetised mongrel dogs, administration of E coli endotoxin caused a rise in plasma met-enkephalin-like immunoreactivity (MLI). Biochemical characterisation of MLI by gel filtration chromatography revealed various molecular forms: 31K, 8K, 3-5K and the native pentapeptide in approximately equal amounts. After enzymatic treatment of column fractions the 31K form predominated (90.7%). This is the first demonstration of elevated MLI in endotoxin shock.

Adrenal vein and arterial levels of catecholamines and immunoreactive metenkephalin in canine endotoxin shock and their response to naloxone.

SummaryThe alterations in plasma levels of immunoreactive metenkephalin (ir-metenkephalin) and catecholamines in adrenal vein and arterial blood in response to endotoxin, as well as the effects of subsequent naloxone administration, have been investigated in a canine model. Animals were anaesthetised with alpha choloralose and allowed to breathe spontaneously. The left lumbar adrenal vein was cannulated and an intermittent choke allowed retrograde sampling of the adrenal effluent. Severe shock was produced by the administration of a large bolus ofE. coli endotoxin (5 mg/kg) followed by a continuous infusion (2 mg/kg per hour). One hour after induction of shock the circulating volume was expanded using a colloidal gelatin solution. Thirty minutes later one group of five animals received a bolus of naloxone (2 mg/kg) followed by a continuous infusion of (1.5 mg/kg per hour), while a control group of five animals was given an equivalent volume of isotonic saline. The production of endotoxin shock was associated with marked increases in adrenal vein and systemic levels of adrenaline and noradrenaline. Naloxone administration transiently limited the fall in adrenal vein levels of adrenaline and noradrenaline (P < 0.05) following volume replacement and was associated with a sustained increase in systemic adrenaline levels (P < 0.05). Changes in mean arterial pressure confirmed a significant haemodynamic response to naloxone (P < 0.05). Alterations in ir-metenkephalin levels in the adrenal vein closely followed the changes in catecholamines, whereas arterial levels rose progressively and were unaffected by naloxone. We conclude that in canine endotoxin shock the opiate antagonist naloxone can transiently increase catecholamine levels in the adrenal effluent and produce a more sustained rise in systemic adrenaline levels. Moreover, the adrenal medulla is not the only source of circulating ir-metenkephalin.