Table 4.

Binding affinity assays of somatostatin-like analogs with opioid receptors

Compound	IC50, nM		μ versus δ selectivity
	Binding versus [3H]DPDPE	Binding versus [3H]CTOP
1. Somatostatin	15,000a	20,000a	0.7
2. D-Phe-c[Cys-Phe-D-Trp-Lys-Thr-Pen]Thr-OH	20,000a	1,000b	20
3. D-Phe-c[Pen-Phe-D-Trp-Lys-Thr-Pen]Thr-OH	9,800a	10,800b	none
4. D-Phe-c[Cys-Tyr-D-Trp-Lys-Thr-Pen]Thr-OH	3,800a	290b	13
5. D-Phe-c[Cys-Tyr-D-Trp-Lys-Thr-Pen]Thr-NH2	950a	3.5b	270
6. D-Phe-c[Cys-Tyr-D-Trp-Lys-Val-Pen]Thr-NH2	2,000	5.5	360
7. D-Phe-c[Cys-Tyr-D-Trp-Arg-Thr-Pen]Thr-NH2 (CTAP)	4,500	3.5	1,300
8. D-Phe-c[Cys-Trp-D-Trp-Orn-Thr-Pen]Thr-NH2 (CTOP)	13,500	2.8	4,800
9. D-Tic-c[Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2	1,300	1.2	1,100
10. D-Tic-c[Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2	16,000	1.4	11,300

^avs[³H]DADLE.

^bvs[³H]naloxone.

Abbreviations: DADLE, [D-Ala²,D-Leu⁵]enkephalin; DPDPE, c[D-Pen²,D-Pen⁵]enkephalin.