William C. Engeland

Splanchnic Neural Activity Modulates Ultradian and Circadian Rhythms in Adrenocortical Secretion in Awake Rats

An ultradian rhythm in adrenal secretion of corticosterone has been described in awake rats using intra-adrenal microdialysis. To determine the role of the autonomic innervation of the adrenal on the expression of the corticosterone rhythm, adrenal extracellular fluid was sampled by intra-adrenal microdialysis in intact (CTRL) and splanchnicectomized (SPLNX) rats 5-7 h before (light period) and after dark onset (dark period). Experiments conducted 1, 2, or 5 days after surgical insertion of the microdialysis probe consisted of continuous collection of dialysate at intervals of 10 min. Time domain pulse detection using PC-PULSAR showed that 5 days after surgery, SPLNX decreased interpulse interval (IPI) during the light period, but had no effect during the dark period, resulting in the loss of the diurnal rhythm in corticosterone secretion. Although diurnal modulation of both pulse amplitude and pulse frequency was observed, only the frequency was altered by SPLNX. In CTRL animals IPI increased at 5 days postsurgery, relative to 1 and 2 days, but the amplitude of normalized secretory pulses did not change. The decrease in IPI caused by SPLNX was observed 5 days, but not 1 or 2 days after surgery, suggesting that surgical stress obscures the inhibitory effect of splanchnic neural activity. Power spectral analysis showed significant periodicities in corticosterone secretion rate in individual CTRL and SPLNX animals at 1, 2, and 5 days. One day after surgery, SPLNX reduced the frequency of the ultradian rhythm detected by power spectral analysis. This finding suggests that splanchnic neural activity may increase pulse frequency in stressed rats, in opposition to the effect seen after extended recovery from surgery. In conclusion, our data suggest that the nadir of the diurnal rhythm in corticosterone secretion results in part from neural inhibitory control. Splanchnic neural innervation may also have an excitatory role in the adrenocortical stress response.

Corticotropin‐releasing Factor in the Adrenal Medulla

Immunoreactive and bioactive corticotropin-releasing factor has been identified in the adrenal gland of dogs, rats and humans. Radioimmunoassay and immunohistochemical experiments have clearly demonstrated that localization of the peptide is confined to the adrenal medulla. CRF-containing cells have a characteristic appearance and are often found in close association with blood vessels. Electron microscopic studies suggest that CRF is secreted at blood vessels within the adrenal medullary vasculature. CRF has also been identified in pheochromocytomas. The amount of the peptide made by such tumors is highly variable as the CRF content of pheochromocytomas may be 20 to 100 times higher or lower than that of normal adrenal tissue. The pathophysiological importance of CRF in pheochromocytomas is unknown. Excessive secretion of the peptide into the peripheral circulation may cause prolonged activation of the pituitary adrenal axis. The peptide may also act within the tumor, although its role remains obscure. Studies on chronically cannulated, awake dogs have shown that CRF is secreted into adrenal venous blood. A gradient exists between adrenal venous and peripheral arterial blood, as CRF is undetectable peripherally under resting conditions. Hemorrhage, a hemodynamic stimulus known to activate a sympathetic adrenal response, increases the CRF secretory rate. The time course of CRF secretion in response to this stimulus parallels that of epinephrine secretion. The physiological significance of adrenal medullary CRF remains to be determined. Although CRF has been shown to affect catecholamine secretion, the peptide appears to be only a weak secretagogue for catecholamines. We suggest that CRF may affect local blood flow within the adrenal medulla and may modify catecholamine secretory rates via this mechanism. The localization of CRF cells in close apposition to blood vessels supports this hypothesis.

The use of immunoradiometric assay for the measurement of ACTH in human plasma

Bioassay and immunoassay techniques for the measurement of ACTH in human plasma have provided sensitive and specific results but have also met with some skepticism as to their reliability in some clinical circumstances. The recent development of a supersensitive two-site immunoradiometric assay for ACTH may resolve sole of the limitations of previous assays and greatly facilitate the evaluation of pituitary-adrenal disorders.

Measurement of blood flow to the adrenal capsule, cortex and medulla in dogs after hemorrhage by fluorescent microspheres

Changes in adrenal medullary and total cortical blood flow after hemorrhage have been described using radioactive microspheres. To assess changes in adrenal capsular and in intracortical adrenal blood flow, a method was used based on microscopic detection of non-radioactive microspheres. Injection of microspheres labelled with fluorescent dyes permitted multiple determinations of blood flow. Pentobarbital anesthetized dogs (n = 6) were prepared acutely with left ventricular and aortic catheters for injection and collection of microspheres, respectively. Adrenal denervation was done unilaterally by cutting the thoracic splanchnic nerve. Injections of 16-microns spheres were made prior to and immediately after 18 ml/kg hemorrhage done over 6 min. Dogs were killed with KCl and adrenals were removed, fixed and sectioned at 80 microns. Using fluorescence microscopy, microspheres were counted in the adrenal capsule, zona glomerulosa, inner cortex (zona facsiculata and reticularis), and the medulla. The majority (95%) of microspheres in the adrenal cortex were trapped in the zona glomerulosa, precluding an independent estimate of blood flow to the inner cortex. Thus, total cortical blood flow was determined by summing the number of 16-microns microspheres in the zona glomerulosa and inner cortex. Prior to hemorrhage, blood flow was greater in the capsule (5.4 +/- 1.6 ml/min/g) compared to the cortex (1.8 +/- 0.9 ml/min/g) and the medulla (2.9 +/- 1.8 ml/min/g). Splanchnicotomy did not change blood flow in the resting state. Following hemorrhage, in innervated glands, medullary blood flow increased to 8.6 +/- 3.1 ml/min/g, whereas blood flow to other zones was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Response to Repeated Hemorrhage: Implications for Studies of Trauma

Endocrine responses to trauma are often inferred from responses seen after a single injury or elective surgery. However, major trauma frequently is followed by emergent surgery, necessitating evaluation of responses to repeated stimuli. We used sequential hemorrhage to study such responses. Splenectomized dogs anesthetized with pentobarbital (25 mg/kg) were hemorrhaged 7.5 ml/kg, 2 days following adrenal vein cannulation. Secretion rates of cortisol and catecholamines were determined in timed adrenal samples by HPLC. The bled volume was reinfused after 1 hour; the procedure was repeated 24 hours later. A significant response in adrenal secretion of cortisol was seen following hemorrhage each day (p less than 0.001), but the response on day 2 was 40% greater (p less than 0.05). Secretion rates of epinephrine and of norepinephrine did not change after hemorrhage on day 1 (p greater than 0.20). However, each hormone showed a dramatic response on day 2 increasing to 14x control levels (p less than 0.005). There were no differences in any cardiovascular variable during control period or after hemorrhage on the 2 days. The results demonstrate dramatic potentiation of the response to a second insult that persists for at least 24 hours after the first, and suggest that the endocrine response to traumatic injury with emergent surgery cannot be evaluated by studying responses either to isolated insults or to elective surgery.