Basal and potassium-evoked release of angiotensin II from the rat hypothalamus

Although the protein components of the renin-angiotensin system have been localized in the brain, it remains to be established whether or not angiotensin II (Ang II) is generated locally and secreted into the interstitial fluid of the brain. We have addressed this issue in vitro by perifusing explants of the rat hypothalamo-neurohypophysial system (HNS) (5 explants per chamber, 37°C) with Krebs solution at a rate of 1 ml/min. The release of Ang II immunoreactivity (Ang II-ir) and arginine vasopressin immunoreactivity (AVP-ir) in the medium was measured 3–5 h after HNS dissection and again after addition of potassium (K⁺) to the perifusate. Samples of the fluid perifusing the HNS were collected for 30-min intervals and concentrated using Sep-Pak C₁₈ cartridges. Release of Ang II-ir was significantly increased during perfusion with 70 mM K⁺ (from 29 ± 14pg/30min to80 ± 17pg/30min, P < 0.01). This increase coincided with a dramatic rise in the release of AVP-ir (from50 ± 35pg/30min to values above2000pg/30min). The associated release of Ang II-ir in response to depolarization by K⁺ is consistent with the hypothesis that Ang II can be secreted by neuronal elements of the brain, possibly via a regulated pathway.     

Magnification radiography in osteomyelitis

Osteomyelitis often eludes early diagnosis because plain film radiography is too insensitive and radionuclide bone scanning is nonspecific. In this study, 90 diabetic patients were studied with plain film and magnification radiographs of their feet. Among the 24 patients with osteomyelitis, plain radiographs suggested the diagnosis in 14 patients and magnification radiography was diagnostic in 18 of these patients. Thus, magnification radiography offers some diagnostic advantage in patients suspected of having osteomyelitis.     

Hemodynamic and neurohormonal changes in the development of DOC hypertension in the dog

In this article we summarize studies of the hemodynamic and endocrine effects of desoxycorticosterone (DOC)-induced hypertension in dogs and also review new data of the action of this steroid on baroreceptors. The hemodynamic effect of subcutaneous injections of DOC to dogs, without supplementation of salt in their diet, consisted of increases in arterial pressure that were sustained for a 28-day observation period and associated with augmented cardiac output. At the early stage of the hypertensive response there was a rise in plasma Na+ concentration accompanied by increases in the plasma and cerebrospinal fluid (CSF) levels of vasopressin. The activity of the peripheral renin angiotensin system, as evaluated by the longitudinal changes in plasma renin activity and plasma immunoreactive angiotensin II (irAng-II), was markedly depressed in the hypertensive dogs. In contrast, the concentration of irAngII in the CSF did not change. Additional studies of the carotid occlusion reflex in anesthetized dogs revealed an enhanced buffering baroreceptor capacity in the early (less than day 10), but not the late (greater than day 28), stages of the hypertension. The abnormality in baroreflex function may be mediated by an effect of the steroid on an activity of brain angiotensin II that influences the inhibitory interaction between high and low pressure baroreceptors. The data acquired in these studies agree with the notion that excess mineralocorticoid production causes hypertension by mechanisms that influence the neurohormonal control of blood pressure by the central nervous system.     

Experienced and Less‐Experienced Nurses Diagnostic Reasoning: Implications for Fostering Students' Critical Thinking

PURPOSE. To compare the use of mental representations (heuristics) in diagnostic reasoning of expert (≥5 years' experience) and novice (<5 years' experience) emergency nurses. METHODS. Clinical simulations were completed by a nationwide randomly selected sample of 173 experienced and 46 less‐experienced emergency nurses (N =229). FINDINGS. Experienced nurses used the heuristic, Judging by Causal Systems (diagnostic inferences deduced from systems of causal factors) significantly more did than less‐experienced nurses. PRACTICE IMPLICATIONS. Standardized nursing diagnoses may cut short the time needed to develop representational thinking and spare cognitive reserves for reasoning needed for complex patients. Faculty need to promote students' cognitive development through strategies that promote active, reflective, and integrative learning. Search terms: Clinical experience, diagnostic reasoning     

Angiotensin II and angiotensin (1–7) excite neurons in the canine medulla in vitro

Our group showed previously that the heptapeptide angiotensin (1–7) [Ang-(1–7)] is a bioactive product of the renin-angiotensin system, and produces dose-dependent cardiovascular effects similar to those evoked by Ang II when microinjected into the nucleus tractus solitarii (nTS) of the rat. The effects of Ang II were compared with those of Ang-(1–7) on single neuron activity recorded from the medial nTS or dorsal motor nucleus of the vagus (dmnX) in perifused horizontal slices of the canine dorsomedial medulla. Ang II excited 48% of 31 medial nTS neurons, but only activated 14% of 22 dmnX cells. Ang-(1–7) also excited half of the medial nTS cells and 14% of the dmnX neurons. Although most medial nTS neurons excited by Ang II were also activated by Ang-(1–7), two cells were excited by Ang II but not by Ang-(1–7), and one cell was excited by Ang-(1–7) but not by Ang II. Because Ang-(1–7) lacks direct vasoconstrictor effects, neurons in the dorsomedial medulla may have different receptor characteristics than peripheral tissues. The observation of a few medial nTS neurons excited by only one Ang peptide suggests that there may be a separate Ang-(1–7) receptor that participates in the physiological effects of Ang peptides mediated by the brain.     

Addison's disease and empty sella

A 47-year-old woman affected by Addison's disease, inadequately treated with corticosteroids for 14 yr, was referred to our clinic. As a x-ray of skull revealed an enlarged sella turcica, a more thorough study of hypothalamic-pituitary function and of the sellar region was performed. The normal suppression of high plasma ACTH levels induced by hydrocortisone infusion and the normal pattern of ACTH, TSH, PRL, LH and FSH to appropriate stimuli (CRH, TRH, GnRH) excluded the possible existence of an ACTH-secreting adenoma; the CT scan images showed the presence of an empty sella. The impaired GH rise after GHRH may be attributed to either the empty sella or the adrenal failure. This is the first patient with Addison's disease and empty sella, in whom the hypothalamic-pituitary function has been studied by the administration of four releasing hormones.