We have previously shown that activation of muscle receptors by passive stretch (PS) increases heart rate (HR) with little change in blood pressure (BP). We proposed that PS selectively inhibits cardiac vagal activity. We attempted to test this by performing PS during experimental alterations in vagal tone. Large decreases in vagal tone were induced using either glycopyrrolate or mild rhythmic exercise. Milder alterations in vagal tone were achieved by altering carotid baroreceptor input: neck pressure (NP) or neck suction (NS). PS of the triceps surae was tested in 14 healthy human volunteers. BP, ECG and respiration were recorded. PS alone caused a significant decrease (P < 0.05) in R-R interval (962 ± 76 ms at baseline compared to 846 ± 151 ms with PS), and showed a reduction in HR variability, which was not significant. The decrease in R-R interval with PS was significantly less (P < 0.05, n = 3) following administration of glycopyrrolate (−8.1 ± 4.5 ms) compared to PS alone (−54 ± 11 ms), and also with PS during handgrip (+10 ± 10 ms) compared with PS alone (−74 ± 15 ms) (P < 0.05, n = 5). Milder reductions in vagal activity (NP) resulted in a small but insignificant further decrease in R-R interval in response to PS (−107 ± 17 ms compared to PS alone −96 ± 13 ms, n = 5). Mild increases in vagal activity (NS) during PS resulted in smaller decreases in R-R interval (−39 ± 5.5 ms) compared to PS alone (−86 ± 17 ms) (P < 0.05, n = 8). BP was not significantly changed by stretch in any tests. The results indicate that amongst muscle receptors there is a specific group activated by stretch that selectively inhibit cardiac vagal tone to produce tachycardia.

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Plantlets of a diploid species, Rosa wichuraiana, were cultured in vitro in liquid medium and treated with spindle inhibitors or tritiated thymidine . Cytological studies were then carried out on cells of root tips which were excised after the treatments . Exposure to 0 .05 colchicine gave complete spindle arrest with less toxicity than 0 .1% colchicine . Solutions of colcemid gave incomplete spindle arrest even at highly toxic concentrations . After a 0 .5 h pulse of 3H thymidine, the periodicity in the curve of percentage of labelled mitoses against time indicated a cell-cycle-time of 10 h . The highest frequency of tetraploid cells was obtained after exposure to 0 .05% colchicine for 12 h and it is suggested that colchicine prolonged the cell-cycle-time by 2 h . Seven days after a 12 h exposure to 0 .05% colchicine, 32.7% of cells in the root meristem were tetraploid and it is anticipated that a satisfactory yield of non-chimeral tetraploids could be regenerated from such tissues .

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