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In order to evaluate disturbances of the respiratory control in the first year of life in children with a statistically enhanced risk of SIDS, substance P-like immunoreactivity (SPLI) in plasma and mean apnoea duration (MA) were examined. 4 groups of infants were investigated: Controls, full-term infants with anamnestic SIDS-risk factors, preterm infants with additional risk factors and preterm infants without such factors. Infants aged from -4(corrected age) to 63 weeks. SPLI in plasma was determined by a specific, homologous radioimmunoassay. The SPLI-level was significantly higher in controls (n = 41; means +/- SE = 36.37 +/- 4.86 pg/ml) than in preterm infants without (n = 21; 25.41 +/- 5.54 pg/ml) or with additional anamnestic risk factors (n = 111; 25.89 +/- 3.09 pg/ml). SPLI was higher in full-term SIDS-risk infants (n = 150; 30.73 +/- 2.35 pg/ml) than in the preterm groups. There is a significant age dependence in the groups full-term SIDS-risk infants and preterm infants with additional risk factors. During maturation the SPLI-level in plasma rises in these groups from lower values. The MA-values were determined by means of a daytime polygraphy. There is an age dependence of the MA-values during active sleep in full-term SIDS-risk infants and in preterm infants with additional anamnestic risk factors. In the age group 4-17 weeks (peak of SIDS frequency) in active sleep the MA-values were significantly higher in all 3 risk groups than in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The substance P-like immunoreactivity (SPLIR) of plasma and adrenal medulla from spontaneously hypertensive (SHR) and normotensive WKY rats was measured by a sensitive and highly specific radioimmunoassay for substance P (SP). With increasing age the level of substance P in the adrenal medulla decreased, whereas the SP content of the plasma remained constant in both groups. The SPLIR in plasma of SHR was significantly lower than in normotensive WKY rats. After acute stress the SPLIR, especially of the adrenal medulla of WKY rats, increases, and decreases in SHR. The reason for this different behaviour is discussed and it is assumed that hyperreactions in the sympathetic system may be responsible.

Substance P-like immunoreactivity (SPLIR) has been found in fibres and the surroundings of ganglion cells and in a new cell type of rat adrenal medulla, using the indirect immunohistochemical method. These SPLIR-cells are characterized by their localization in the connective tissue in close vicinity of vessels and by acidophilic staining in HE-procedure. Relationships are discussed between the localization of substance P in the adrenal medulla and possible interactions with catecholamines with respect to stress.

Bronchoalveolar lavage was performed in guinea pigs during bronchial challenge with capsaicin (100 micrograms/kg b.w. intravenously) and in control animals. Capsaicin caused a bronchoconstriction (VT minimal: 27.17% +/- 24.49). There was a significant amount of substance P-like immunoreactivity, detected by RIA in the lavage fluid of four of five animals challenged with capsaicin, but only in one of five controls. These results indicate that SPLIR is released into the bronchial lumen during capsaicin-induced bronchoconstriction. So bronchoalveolar lavage may be a useful tool to investigate the role of substance P in the bronchoconstrictor response induced by various stimulants.

Patients with essential hypertension (n = 45) had significantly lower substance P plasma levels (13.6 +/- 2.30 pg/ml) in comparison with a group of 24 normotensive subjects (45.4 +/- 7.18 pg/ml) analyzed by radioimmunoassay. Prazosin treatment for 2 weeks with 4.5 mg/day enhanced the substance P plasma level depending on its antihypertensive effect. Norepinephrine concentration in plasma was also elevated by prazosin. Dipeptidylpeptidase IV, dopamine-beta-hydroxylase and plasma renin activity were not changed significantly. The results indicate the participation of substance P in pathophysiological processes of human essential hypertension.

The influence of chronic immobilization on blood pressure and on substance P-like immunoreactivity (SPLIR) in blood plasma was examined in 11-week-old male spontaneously hypertensive rats (SHR) and male normotensive Wistar Kyoto rats (WKY). In SHR chronic immobilization caused a stop of the genetically fixed development of hypertension at the level already reached. Also, SPLIR in blood plasma was lower compared with a SHR control group without immobilization. In WKY rats chronic immobilization has no influence on blood pressure and SPLIR. The observed variations in SPLIR and blood pressure under the influence of chronic immobilization is discussed in relation to a possible function of substance P in the development of hypertension.