Coeficiente de Cobertura de Liquidez

Fast sal P 0.3 G 0.8 P 0.3 + G 0.8 0

20 40 60 80 100

VAS rating at 120 min (mm)

Figure 2.4 Meal Palatability Rating Following Ad Libitum Lunch in Dose Verification Study

Six healthy subjects underwent 90 minute infusions of saline (Fast sal), 0.3 pmol/kg/min PYY3-36 (P 0.3), 0.8 pmol/kg/min GLP-17-36amide (G 0.8) and combined 0.3 pmol/kg/min PYY3-36

+ 0.8 pmol/kg/min GLP-17-36amide (P 0.3 + G 0.8). All subjects were fasted overnight before each study visit. An ad libitum buffet meal was served immediately after the infusion and subjects retrospectively rated its palatability on a scale of 0-100.

62 2.3.3 Total Plasma PYY Levels in Dose Verification Study

Mean plasma concentration of total PYY(from time points t= 15 min to t = 90 min) was 27.48 ± 1.7 pmol/L when saline was infused, 66.78 ± 9.0 pmol/L when 0.3 pmol/kg/min PYY_3-36 was infused, 20.5 ± 0.4 pmol/L when 0.8 pmol/kg/min GLP-1_7-36

amide was infused, and 87.29 ± 8.8 pmol/L when the combination 0.3 pmol/kg/min PYY_3-36 + 0.8 pmol/kg/min GLP-17-36 amide was infused.

Peak mean plasma concentration of total PYY(during the entire study) was 33.26 pmol/L when saline was infused (occurring at t = 30 min), 91.07 pmol/L when 0.3 pmol/kg/min PYY3-36 was infused (occurring at t= 90 min), 33.3 pmol/L when 0.8 pmol/kg/min GLP-17-36 amide was infused (occurring post-prandially at t = 120 min), and 106.5 pmol/L when combination 0.3 pmol/kg/min PYY3-36 + 0.8 pmol/kg/min GLP-17-36 amide was infused (occurring at t = 90 min).

There was no significant difference between plasma concentration of total PYY achieved between saline and GLP-17-36 amide 0.8 pmol/kg/min infusions. Furthermore, there was no significant difference between mean plasma concentration of total PYY achieved when PYY_3-36 was infused singly or in combination with GLP-1_{7-36 amide}. This was true for repeated measures analysis over the whole study (i.e. t = -60 to t = 120 min) as well as for repeated measures analysis for samples analysed during the infusion period (t= 15 to t= 90 min). Figure 2.5 shows the variation of plasma total PYY levels with time in the Dose Verification Study.

63

-90 -60 -30 0 30 60 90 120 150

20 40 60 80 100

120 Fasted saline

PYY 0.3 pmol/kg/min GLP-1 0.8 pmol/kg/min PYY 0.3 + GLP-1 0.8

Time (min)

Total Plasma PYY(pmol/L)

Figure 2.5 Plasma Total PYY Levels During Dose Verification Study.

Six healthy subjects underwent infusions of saline , 0.3 pmol/kg/min PYY_3-36 , 0.8 pmol/kg/min GLP-1_7-36amide and combined 0.3 pmol/kg/min PYY_3-36 + 0.8

pmol/kg/min GLP-1_7-36amide . All subjects were fasted overnight before each study visit. On each visit, the infusion was administered between t= 0 and t= 90 min, after which lunch was immediately served.

64 2.3.4 Total Plasma Amidated GLP-1 Levels in Dose Verification Study

Mean plasma concentration of amidated GLP-1(from time points t = 15 min to t = 90 min) was 19.8 ± 0.2 pmol/L when saline was infused, 17.2 ± 0.5 pmol/L when 0.3 pmol/kg/min PYY_3-36 was infused, 58.9 ± 6.0 pmol/L when 0.8 pmol/kg/min GLP-1_7-36

amide was infused, and 59.4 ± 5.7 pmol/L when the combination of 0.3 pmol/kg/min PYY3-36 + 0.8 pmol/kg/min GLP-17-36 amide was infused.

Peak mean plasma concentration of total amidated GLP-1 (during the entire study) was 32.4 ± 4.7 pmol/L when saline was infused (occurring post-prandially at t = 120 min), 26.3 ± 4.0 pmol/L when 0.3 pmol/kg/min PYY3-36 was infused (occurring post-prandially at t= 120 min), 73.3 ± 6.7 pmol/L when 0.8 pmol/kg/min GLP-17-36 amide was infused (occurring at t= 90 min), and 73.0 ± 9.4 pmol/L pmol/L when the combination of 0.3 pmol/kg/min PYY_3-36 + 0.8 pmol/kg/min GLP-17-36 amide was infused (occurring at t = 90 min).

There was no significant difference between plasma concentration of total amidated GLP-1 achieved between saline and single PYY_3-36 infusions. There was also no significant difference between mean plasma concentration of total amidated GLP-1 achieved when GLP-17-36 amide was infused singly or in combination with PYY_3-36. This was true for repeated measures analysis over the whole study (i.e. t = -60 to t = 120 min) as well as for repeated measures analysis for samples analysed during the infusion period (t= 15 to t= 90 min). Figure 2.6 shows the variation of plasma total amidated GLP-1 levels with time in the Dose Verification Study.

65

-90 -60 -30 0 30 60 90 120 150

0 20 40 60 80 100

PYY 0.3 + GLP-1 0.8 GLP-1 0.8 pmol/kg/min Fasted saline

PYY 0.3 pmol/kg/min

Time (min)

Total Plasma Amidated GLP-1 (pmol/L)

Figure 2.6 Total Plasma Amidated GLP-1 During Dose Verification Study Six healthy subjects underwent infusions of saline , 0.3 pmol/kg/min PYY_3-36 , 0.8 pmol/kg/min GLP-1_7-36amide and combined 0.3 pmol/kg/min PYY_3-36 + 0.8

pmol/kg/min GLP-1_7-36amide . All subjects were fasted overnight before each study visit. On each visit, the infusion was administered between t= 0 and t= 90 min, after which lunch was immediately served.

66

2.4 DISCUSSION

The combined infusion of 0.3 pmol/kg/min PYY_3-36 + 0.8 pmol/kg/min GLP-17-36 amide

led to a statistically significant 32% reduction in ad libitum energy intake during the test meal compared with the control saline visit. This was associated with a small and tolerable rise in nausea ratings – notably only recorded on the written VAS scoresheets and never verbally reported during the infusions by any subject, or severe enough to necessitate discontinuation of the infusion. Single infusions of each of the hormones at these doses appeared to have no effect at all on subsequent energy intake in this small group of healthy volunteers, and also produced no nausea.

A peak mean plasma total PYYconcentration of 106.5 pmol/L and total GLP-1 level of 73 pmol/L was achieved during the combined 0.3 pmol/kg/min PYY_3-36 + 0.8 pmol/kg/min GLP-17-36 amide infusion. In the previously cited paper where combination 0.4 pmol/kg/min PYY3-36 + 0.4 pmol/kg/min GLP-17-36 amide were co-infused, the peak circulating PYY and GLP-1 levels reported were 58.4 pmol/L and 62.5 pmol/L respectively (Neary et al., 2005). These discrepancies may be partly due to the fact that the doses used in this study were adjusted for the peptide content of the prepared vials. Furthermore, there is likely to be a degree of inter-assay variation. Circulating plasma hormone levels fell sharply (more so for GLP-1) back towards baseline within 30 minutes of discontinuation of the infusions, adding weight to the decision to serve the test meal immediately after termination of the infusion.

67 Although limited by small sample size, the results from this dose verification study were reassuring. At the chosen doses of 0.3 pmol/kg/min PYY_3-36 and 0.8 pmol/kg/min GLP-1_{7-36 amide},single gut hormone infusion was subanorectic, combined gut hormone infusion significantly reduced food intake without inducing serious nausea and the plasma levels achieved were in line with the literature. These doses were taken forward into the functional neuroimaging study described in the next chapter.

68

CHAPTER 3

Investigation of the Effects of single